There is no fast easy way to make good glass parts. It is a three part process. Plug, Mold, Part. The surface finish will not improve at the completion of each stage. The finish on the plug determines the finish on the part. The high gloss finish in the mold is not just for show. The gloss finish is a big factor in the release of parts from the mold.

So, paint the plug with a good quality paint, enamel, auto, etc etc. Polish and buff it to a high gloss. Wax the plug with Mold Release wax, Then apply the gelcoat.

The picture shows a reasonably good mold surface.

Ed S