[Rick TYler]

Arthur's advice is excellent. If you can repair the fin off the rocket, you might lay the fin on a piece of polyethelene plastic (the plastic sheets sold in rolls in home centers are mostly poly) create your repair with epoxy and fiberglass stiffener, squeegee out the excess epoxy, and the cover it with another layer of poly. Place a large flat weight on top of this sandwich and you will end up with a smooth, no-sanding-required surface.

Alternately, you can replace the poly with release fabric, which would "suck up" the excess epoxy in your laminate. Since you probably don't have any release fabric, you can just forget this part.

Good luck.