Do it right. pick up a bottle of micro ballons at TAP plastics $5. Get a small tube of slow cure Epoxy from lowes or any where else $3. mix the epoxy with enough microballons to give it a real thick peanut butter consistancy. Fill the holes and cover with either wax paper or saran wrap and shap it to your hull. let it cure then lightly sand it. The ballons should make the color close to your gel coat color if its white. If you want it perfect pick up some gel coat repair at TAP while you are there.