One of the best Epoxy-based fillers is Superfil which Aircraft Spruce sells. It's two part and very light. You can use it to rough in areas like fillets or damaged areas and then fill in with glazing putty and primer to fill in any small holes. Superfil takes 8 hours to dry. If you have a real small area to fix as I get from your message states and there is no foam showing, I would seal off the area with CA or epoxy and then fill over it with spot putty or similar.

Michael