If I had to guess, since there is no picture, I'd assume that 1) the paint, did exactly as you stated, and dried somewhat before it hit the surface creating a rough, pebbley texture or 2) the gloss coat did the same thing, or 3) the surface of the plastic was not properly prepared for painting and there are dust, hair or other foreign materials on the plastic. One thing I always try to do before I apply a gloss coat is to check the paint surface first, if it feels rough, then I will use a fine sanding pad or sanding stick and smooth out the paint, at this point it is possible that I need to apply another light coat of paint. Proper surface prep of the bare plastic is essential as well. I like to wipe the plastic down with a soft, lint-free cloth dampened with 91% isopropyl alcohol.