Is the epoxy still green? I did the same thing on my inside seam tapes on my S&G. The best thing I've found is a little hand held Craftsman Scraper with interchangable blades. The blades come in all different shapes and sizes. A flat one isn't the best cuz you migh cut into the fabric too much.
Just keep scraping till it looks good. Some people on this board have mentioned using pieces of broken glass. I've never done this but, It sounds like it would make short work of it. Be sure to wear heavy gloves.
Dont wait till the stuff hardens all the way! If you get it while it's still green, It will come up easily. I cleaned up a mess on my seams in a few hours.
It's pretty important to get it off if you are going to put another layer of glass down. the epoxy in the middle will weaken matrix. At any rate, it's not adding any strength. Just weight.
Hope this helps!
-David