The average automotive fiberglass repair kit has a resin/catalyst combo that requires air exclusion to finish kicking off the surface.
Polyester resins which are meant to surface cure will use a catalyst with a "surfacing wax". The kit you got probably came with plastic sheet of some sort, and instructions to squeegee the plastic ove top of the repaired area and LEAVE IT ON for at least 4 hours.... (excluding air)
You can catually finish kicking it off by just waxing it. Then use a wax remover and then sand the surface prior to painting.