I have done the same thing, but with a 10 gallon tank. The key is to take it very slowly and to make sure that the edges are free. On tank that I broke, I did so because I was being too impatient. The key is really to keep it slow and not to use too much force.
I have had success with using a dremel for cleaning up the edges, you just have to be careful not to marr the glass underneath.