Review of my first PCB design for a current meter shield
Caveats

Before I begin, I should point out that with mains electronics there is a lot which you can do wrong.  If you want to be sure that it is safe and correct, you'll need to go through an appropriate standard, such as EN61010, and make sure you meet every point.  For something you plan to sell, it would be usual (in some countries) or legally required (in others) to have a professional check it against the standard.  It is unlikely that answers here are ever going to pick out every possible problem. If you are starting out in electronics and looking for hobby projects, I would strongly suggest you don't start with mains electronics.  That said, here's some pointers.

Style

It would be easier to read your schematic if the lines connected the parts a bit more.  It's OK to label two things the same and not connect them on a complicated schematic, but it's not necessary here. On this site, good schematics get good answers.

Your PCB has some silkscreen labels on top of a pin (3.3V).  That's not going to be any use.

Component choice

I haven't looked at much beyond the ACS712.  There are some issues there:


It is going obselete.  For a new design, you should use something which isn't.
It has a 2.5kV isolation.  That may or may not be enough.  Mains supplies in houses (known as overvoltage category II) can have very large spikes.  If that isolation is the only thing between an accessible part and the mains (reinforced insulation) then it needs to be more than 3000V.  If it is one of two or more layers (basic insulation), then each layer must be 1500V or more.  Probably the box counts as a second layer, as long as none of the digital circuitry sticks out.
With a 1nF capacitor you have set a filter frequency of 90kHz.  Do you really want that? You need the filter frequency to be less than half the frequency you plan to read the ADC at.


Fault protection

What happens if the object downstream fails?  What happens if something in the box fails?  You can get huge currents from a wall socket for some time before the circuit breaker trips, and this can cause fires.  You could make this much safer by adding a fuse at the input.  You should then design all the tracks to carry, say, double the value of the fuse.

Clearances and Creepages

For basic insulation in mains overvoltage II, you need 1.5mm. You seem to have that.  For reinforced insulation, you need 3mm. You also seem to have that.  Good.  There is no reason not to have a bit more clearance between some of the mains tracks, so you might as well.

Flammability

The big plastic connectors for mains in and mains out, the plastic box, the PCB and the AC/DC converter should all have good flammability ratings.  Look for UL94 v-0 in the datasheets of the connectors and PCB material, and EN60950 on the converter.  This is important because the mains connections can easily provide enough energy to start a fire, so you need to make sure that it can't spread.  A metal box is also good from this point of view, but then you need to get grounding right so plastic is easier.

I don't have time to add more, but I could go on.  Hopefully you'll get some more answers too