Depends on the level of repair you're after. If a 5' repair is acceptable (you won't notice it from 5 feet or further away), I would probably use Marine Tex on a spot like that. Clean it with acetone, wear gloves (so you don't make the Marine Tex any darker with dirt/smut while kneading it), and apply it leaving it a little above the final surface. As it hardens, you can shape it a little with a razor blade. Once it's fully hardened give it a final sanding and you'll have a good 5 to 8' finish.

If you want a 2' finish, you should probably fill and smooth with bondo, then spray or brush gelcoat on top of that and seal with plastic or PVA. Then wetsand, wetsand a little more...realize you sanded away all the gelcoat and have to spray again...then wetsand a little more, and buff for a great shine and perfect repair. It will be difficult to build up gelcoat alone on that area that thick so you'll probably need to first fill it with bondo (as built, it was originally sprayed that thick in a female mold before the fiberglass and resin were added).

However, I seem to recall that one of those generic gelcoat repair kits had the gelcoat in a really thick form...that might just do (but you have to add the tint to the gelcoat to get the color right).