Take a whettstone to the sharp edges. It happens to everybody so don't fret. Lifting or placing glass to tool is a delicate operation where chipped corners often occur. Beveling the mirror edge helps. A little dish soap in the water and plenty of water to float tool and mirror apart also helps. Broken down grit and ground glass makes such a sticktion paste in the fine grinding stage and pulling them apart is the main cause of chipped edges.
-Rick