Gel coat doesn't cure completely when exposed to air. After sraying it on, you should spray a light coating of PVA (poly vinyl alcohol - mold release agent) over it to seal it up while it cures. After the cure, the PVA can be washed off with water. There are also additives that you can mix with the gel that form a protective film while the gel is curing to allow for a complete cure.

For your particular problem, I'd spray another light coat of gel over the tacky section and use the PVA as described above to get it to cure completely.

There's a good article on re-gelcoating here.