Scratches can sometimes be buffed out of fiberglass as long as the scratches are not too deep in the fiberglass.
For scratches in the fiberglass that don't penetrate down into the layers of the fiberglass they can usually be wet sanded and buffed out.
Deeper scratches will require and epoxy and then be wet sanded to get rid of the deep scratches in the fiberglass.
Before filling in a deep scratch in the fiberglass wet sand the deep scratch to smooth the outer surface and to give the epoxy a rough surface to adhere too.
After sanding the surface of the fiberglass put the epoxy on in small thin layers and then after the fiberglass repair epoxy dries then you can wet sand it.