How can I make it clear to other road users that I'm an inexperienced cyclist?
This is an interesting and thoughtful question, and just the fact that you are thinking carefully about how other road users think about you is very valuable and will contribute to your safety on the road.
Your question makes a lot of sense. How do you indicate to drivers that you need and deserve their consideration and patience, especially when you have doubts about your own skill on the bike and the road right now?
Unfortunately, I am not sure that being seen as inexperienced will result in drivers being more considerate. I think it is likely to have the opposite effect. Just look how impatient and inconsiderate drivers can be when dealing with a learner driver who holds them up or inconveniences them.
Even children, unfortunately, don't in my experience get treated with more patience or consideration.
My warning would be that making your inexperience clear to other drivers is likely to have negative results.
Three points
Instead, I believe that the key things are to be:

noticed - the driver has to see you in the first place
thought about - can you give the driver reasons to think more carefully about you?
respected - can you give the driver reasons to consider your value and needs?

One of the best things I've read to help think about this is David Martin's Theory of Big. I won't repeat its points here, but I think it's well worth reading.
Regarding those points above:
To be noticed
Are you brightly lit, visible, do you stand out, catch eyes? Do you ride in a visible position, make clear, large signals? How do you dress, and move?
Mostly, these are easy things to do. Riding in a visible position needs confidence though; that's not always so easy.
To be thought about
It's not enough merely to be noticed. You want to take up some space in the thoughts of drivers. What can you do to achieve this?
Unfortunately, once again it often does take some confidence to ride in a way that helps you get thought about.
For example, on a road that I know has pot-holes or gravel in awkward places, I will ostentatiously signal and move widely around them; this can help a driver think &quot;oh, this person moves around and does stuff&quot; (not: &quot;I can slip by this cyclist without a moment's thought or without leaving much room&quot;).
If you need to signal, signal in big, clear, impossible-to-miss ways that look like they express meaning. What you signal are your intentions. The physical act of signalling will get you noticed, but the expression of your intention is what will get you thought about.
More: at a traffic light on a busy road, if I am stopped in front of a car, I might pretend to fiddle with a brake or pedal or gear, or tug at the strap of a pannier, just to occupy some attention of a driver while we wait for the lights to change (when? sometimes I just get a feeling that this might be a useful thing to do).
Or, if I spot an on-coming car on a narrow country lane, I will make sure to move clearly across the line of sight of the oncoming driver before slipping in to the side of the road to make room. I don't disappear into a hedge before the driver has seen me.
Generally, you want to ride in ways that are cautious and predictable but without appearing to be too predictable. If a driver is sure that they know what you will do, that can be very dangerous. Better that they are never entirely sure what you will do, so that they stay alert for what you actually do.
I try to look as though I might do something that needs them to respond to appropriately. I want them to imagine that the wheels might suddenly fall off my bike, that my bags might burst open strewing shopping in their path, that I might suddenly stop to admire a flower or greet a friend.
It's important to note: I am absolutely not recommending foolish or dangerous behaviour. Weaving around unnecessarily around other road users is dangerous. Doing unpredictable things is dangerous. Riding on unreliable equipment can be dangerous. Actually having a loose bag is dangerous.
There are two more important ways that help you get thought about. They are to:
Make strong, clear eye-contact
Eye-contact is valuable. You exchange a lot of information - for example, you can communicate an intention - but you also simply place yourself in another's thoughts by it.
Avoid eye-contact
Sometimes, the opposite is called for. If a driver thinks you haven't seen them, they will be thinking about you and wondering what you will do. That's exactly what you want. So sometimes, I studiously avoid catching a driver's eye.
Which of these two techniques you adopt in any particular case will depend on the precise circumstances; I'm not sure I could formulate a clear rule. Both require and demonstrate a kind of confidence.
But either way, you don't want to appear as an uncertain, diffident road-user whose intentions and future actions are of no consequence and don't need to be thought about.
To be respected
Finally, you need to be respected. There are two senses to being respected:
You need to be respected as a human being
People, mostly, will recognise and respect another's humanity. Show that you are a human being, a being like them, to whom they have a duty of care.
The acts described earlier that help you get thought about flow directly into this. Now, as well as being thought about as a road user or as another vehicle on the road, you want to take another step, to be thought about as a human being.
So do human things, and look human.
I might take my hat off (I don't bother wearing a helmet, but it's not a discussion I'm much interested in having) and scratch my head on a long downhill stretch. &quot;Oh,&quot; thinks the driver, recognising that I am a person just like them, &quot;that person has an itch.&quot; Or I will tuck my top in, or pull it out. I might blow my nose at the traffic lights. Something that shows that I have a human body will never be to my disadvantage.
I'm not suggesting to make your bike rides into an unrelenting pantomime of extravagant gestures and unnecessary actions. You don't need to put on any kind of absurd performance (which in itself would be dangerous). It's rather that what you do, when you do it and who you do it in front of makes a difference, so you need to think about it, and use it to your advantage.
You need to be respected as a respectable road user
As well as automatically deserving respect as a human being, which you'd hope would be recognised by all, it also helps to earn respect. Maybe this shouldn't be necessary, but unfortunately, it often is.
Ride politely and considerately. Obey the rules of the road, and make a point of doing so. Stop at lights. Courteously invite motorists to pull out or pass when it's safe to do so.
If a driver makes way for you, make it clear that you thank them. Don't just wait to notice it, try to catch drivers in the act of being considerate so that you can acknowledge it.
Finally, people often respect people who behave as though they deserve respect. That is a good way to ride: confidently, as though you belong on the roads, as though you expect their consideration and respect. Diffidence and uncertainty will unfortunately lose you that respect from some drivers. Act confidently - such as making signals and decisions - even when you don't feel like it, or at least, as much as you can.
This is why I think that advertising your inexperience can do you more harm than good.
It's really hard to do many of the things that I have advocated above. They take confidence, and experience, and practice. Many of them involve demonstrating your vulnerability as a road user, but not your weakness.
I hope this helps, and I hope it helps think about how you need to appear in the eyes of other road users.
I wish I could offer more useful advice about how to do this, for a person who doesn't know already how to. In the meantime, I hope you enjoy your riding and acquire the confidence you're looking for.