I've screwed up my share of paint jobs over the MANY years that I've been building rockets....started out screwing up with model airplane dope.
Too much paint is the biggest error with paint followed by incompatability of different brands.
Do this. first off wait about three or four days. Put the rocket someplace where you will forget about it for a while.
After a GOOD length of time smell the rocket closely...if you can still smell fresh paint, leave it for another couple of days.
When it seems really cured, not just dry, begin by wet sanding with like a 220 grit wet/dry sandpaper. (the black stuff) Sand lightly...let the sandpaper do the work...don't try to grind the paint off. Sand light enough that you can feel the bumps as the sanpaper goes over them.
Use a paper cup with water in it and keep the sandpaper wet, rinsing it every few strokes. Keep paper towels handy and continually wipe the rocket off to check your progress.
If the paint balls up too much stop and let the rocket dry for a few more days....I know this is a pain but ya gotta do it to fix your oops. Also try too avoid sanding the GOOD parts, without extra paint, too much 'cause you'll make the cardboard "hairy" and you'll have to reseal those parts.
I know this is a tuff thing to fix but believe me we've all done it.
When ya get the big bumps off go to a finer grade of sandpaper like 320 grit and all the way to 600 grit if ya wanna get real fussy. Use your fingers to lightly FEEL the finish.
When you feel it is ready to repaint USE THE SAME KINDA PAINT!!!
If ya don't it'll bubble up and ya gotta start over...I've done it. I know!
Do light misty even coats about 1/2 hr appart...don't rush, that's how ya got in trouble the first time. Read the can if you have doubts.
Be patient...you can fix this...don't give up...I have confidence in you!
And report back on your progress.
Don't feel bad. Everybody here has done this.
good luck,
sandman