OK so the mould should be sanded smooth then sealed with a durable paint/epoxy then sanded, then polished with finer and finer grades of paper and polish till its like glass.
Then million coats of wax and buffing.
Then.. Ditch the underside mould and get some mylar and a vacuum pump (like a fridge pump).
Apply a layer of resin/ gelcoat with a roller or spray gun and let it go green before you lay on the cloth.
Do the cloth and resin thing then place in a mylar bag that you made earlier.. Seal up any holes with duct tape and tape in a hose to ur vac pump.
Have a vac tank catch can thing inline so any excess resin is caught before it goes into the pump.
Sorry if telling you to suck eggs but vac bagging is really the only way you will get a light and strong professionally looking piece.