It sounds like porosity more than over spray. Basically very small air bubbles formed in the gel coat while it cured, as you buff the area you are exposing the air bubbles making them more visible. It's not a structural issue (at least I've never seen it be) but cosmetically its not great.
I'd say contact your dealer and see if they do any gel coat work in house, or if they sub it out who they sub it out to. Usually you'll need to remove the affected area, respray and then get to work finishing it all up to look like factory.