You must absolutely remove any surface coating on the "old" finish ie.
your wet out coating of the wood. Sanding with 80 grit paper should to the trick. The problem is that it easy to be a little to enthusiastic and sand to much.
In the future I would use peelply on the surface after you put the epoxy on it. This will soak up excess resen and when it is pulled off it leaves a coarse "tooth" for the next layer to bond to.
A note on fiberglass, you should use the finish (on the glass) that is designed for your resin. Silane finish for epoxy resins.