Refinishing hull on older boat

[twisted t]

My son and I are working on his 14 foot cc for a winter project.Boat is a fiberglass Rodeo(comparable to whaler hull style). Got boat cheap but lots of glass damage and major fading and yellowing. we have filled all holes and scratches with marine tex epoxy and mabey I made a mistake but we have also sanded the hull sides with a power sander and 220 grit paper. Using 600 grit and wet sanding did not come close to removing yellowing etc. Hull sides are now nice and white and I have sanded again with 600 grit wet but I cant get the glossy finish back even after waxing. Do I do more wet sanding or is there a product I should reapply to hull sides such as gell coat repair kit only in larger quanties. Thanks Don