It's tough to know if the abrasion layer is floating or the initial layer of glass is floating too. Only a little experimental sanding will tell you that. If you find that in order to level the glass you are sanding into both layers of glass you have some unfortunate choices.

1. Sand the hull level and add another layer of glass or patch the areas you sand through.

2. live with it. Do a light sanding, get it smooth and varnish it later.

3. Use a heat gun and remove the glass. Sand the hull and re-glass.

Hindsight. In the future you should squeeqe as you go along. It's had to imagine the epoxy getting so thick you couldn't force it out of the weave with a squeege.