One typically fills in chips and dings in gelcoat with gelcoat. I wouldn't use bondo, nor would I use any other type of filler like that unless I were going to paint
. Gelcoat is about the only thing that you can use to blend right in with other gelcoat (and indeed, there's no reason not to use gelcoat).
Here is a link to an article explaining the process (geared towards boats but there is no practical difference):
I also see that there are some "gelcoat repair" videos on You Tube, but I can't watch them on this computer, so I can't recommend or "un recommend" them.