Qcell is your friend here.
Buy a ding repair kit, mix up some qcell and fill that sucker up.
Sand it first with 80 grit dry paper, really give it a good sanding!
Mix resin and qcell, 70/30 mix 70% resin 30% qcell, mix together with a drop of hardener. It should be like car bog.
Sand it down flat so the repair is lower than the rest of the board. Then cut a bit of glass mat to suit and mix some resin to cover the repair.
I use a small paint brush to apply the resin to the cloth, dont be afraid to build up the resin and try and keep air bubbles out.
Let harden and sand with a sanding block until flat and you are done