Travis, I wouldn't worry about sanding the thick areas until I got the other areas filled. Sanding thick epoxy is easy. When you say dry I am assuming that the cloth was completely wetted out in the first coat but not filled. If thats the case, just scuff the area lightly with a scotch bright pad and then epoxy it out. As long as it was wetted out it should be sound, filling the weave is only cosmetic. If it's truly dry (Still white) and not bonded to the wood you may need to cut the glass and add a patch in order to get it to bond to the wood properly.