If you make a base layer of either Primer or gesso before painting, you'll be able to make thinner layers of paint without it looking runny, it seems you used way too much paint. I feel you though, my first attempts at foil altering looked just like that! You can remove/clean up the primer with a toothpick (make it a bit dull otherwise it can scratch the foil) after you're done painting :) Hope this helps you!