I use white gel-coat repair, comes in 2 tubes, mix equal lengths and use as a filler. It gives a perfect repair, it's the same stuff!
In the UK it's made by Plastic Padding, must be an equivalent available over there.
Plastic Padding Gelcoat Filler 165g | sailboats.co.uk
Try a boatyard.
Painting on top gives a different effect as the gelcoat is coloured right through.