80 Grit on a random orbital sander should do it.  Cahnge the paper often and keep the sander moving so you do not gouge into any one area.  The instructions are always to keep the sander flad on the surface.  I often find mysel working the tough spots with the edge of the disk - don't tell the purists-  You can get in trouble doing that.

How long has it been since you put the glass and epoxy on?  The longer it cures the harder it gets however I think mine had been sitting about 6 months when I finally sanded it and it still all came off eventually.

Paul G

Like Paul said... take some 80 grit and go nuts.  Word of caution though: be careful with how much you're taking off.  It is very easy to go too far, and go through the glass.  Because the deck glass is only 4oz, I noticed that I went through it in some spots while fairing the overlap.  And yes, I used the edge of my ROS also, but you need to have a good feel of how much you're working that disk or you can quickly go beyond the point of no return.  IF, and that's a big IF, you do that, make sure you're going over the whole area with the flat pad after so as to level things out as best you can.  Depressions caused from focusing on one area too long can easily show up under paint or varnish.  After I was done with all that sanding, I laid on two more coats of epoxy on the whole boat to make sure that any 'oops' areas got covered, and the hull/deck glass joint disappeared seamlessly.  

Good luck,

~Chris 

Since we're confessing here, I also use the edge of my ROS but I have several hundred hours of "feel" for it. Chris brings up the most important thing here, aside from being careful to not go thru both layers of glass, and that's to get a couple of fill coats on after initial sanding to fill in the imperfections and then do a final sanding with 150 to smooth everything out. Following that with 220 will make it ready for varnishing.

George K

I have found that a carbide paint scraper like this one I got online from Home D is great:

http://www.homedepot.com/h_d1/N-5yc1vZ1xh8/R-100145658/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

It was one of my favorite tools when I did my Shearwater for feathering edges and bumps once you get just a start on the peaks with 60 or 80 grit on a sanding block (I did my whole boat by hand down to 220 - wasn't THAT bad and I never got into the cloth or had to put on another skim coat of epoxy, just the initial coat and then 2 fill coats like the instructions said and then sanded/scraped)

The nice thing about the scraper was that it only took off the high parts and just the right amount at a time so I never worried about getting into the cloth.

Good luck!

Kathy