Cracks on Sheetrock joint compound
The joint compound you used was either not mixed properly or had already dried out to some extent before you applied it.   It also looks like you exacerbated this by putting on a really thick coat.   (also I see the edges and I don't see tape nor joint compound... you mud the edges of your sheet first not the middle)
I personally would try to scrape as much of that off as possible.  Immediately.   If you leave it you will either:

Sand the crap out of it, chunks might come off, and if everything goes as well as possible you still have huge divots/lines.   You will then need to add a few (much thinner coats).

Just add more joint compound and push them into cracks.   They won't perfectly fill cracks and then after you sand for a long time it still won't be smooth.


What you should do...

scrape it off
only add joint compound to the area below mesh tape and a couple inches to each side
your joint compound should be consistency of a runny peanut butter (if you eat Nutella, like a new jar... not the crusty Nutella in an old jar).
after two layers around the tape you can try to add small, smooth layers to center... probably two more to get it right.   You can't just slop on the stuff in the whole area unless you are very skilled and are using a very loose/runny mix.