Acetone will remove the stickiness, as it will remove any uncured resin. After you use the acetone, put another thin layer of resin over it with a very high amount of catalyst. You must be quick, but the extra catalyst and heat created should kick off the remaining resin. This assumes that there are some parts of the original resin that have cured. From you description it sounds as if this is the case. I have had this problem in the past when working on my boat, and I used the method that I explained above to take care of it.
Good luck.
Kurt

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.