If the marks are black (as in it rubbed down to the black fiberglass underneath) then you may be screwed. First try using Softscrub on the areas to make sure it isn't surface marring (paint from something else that rubbed off on it).
I'm currently repainting my Astro City 2, beause it has to many scratches down to the black fiberglass, and let me tell you this is no easy job. I'm using Krylon Fusion spraypaint as its supposed to bond to all types of plastics. It doesn't seem to bond with this fiberglass very well.

The paint came out flat, with an orange peal texture. I followed the instructions exactly, and if you don't put on the next coat withint 24hours, you have to wait 7 days. 2 months later, I finally have everything painted, and am applying a clear acrylic coat to protect it (since it really didn't "bond" to the fiberglass"). I'll post pictures on BYOAC website when I reassemble everything.