Ideally you want to remove that glass/resin overhang when the resin is in the "green state". The green state is when the resin is dry to the touch but still a bit soft. It is within the first 48 hours of application (depending on type of hardner, and curing temperature.) But since that ship has sailed I would suggest 1.) a pair of heavy duty shears (that can be sharpened, because you will dull them considerably). 2.) or, orienting the razor knife such that you push the glass against the wood as you pull it along. I either case leave about a 1/8" edge of glass/resin and remove the rest down to the wood with sandpaper or a block plane.