Trimming off the Excess Glass
After you have wet out the fiberglass and the epoxy has set, you can trim off the excess 'glass. This is easiest done as soon as the epoxy has set up to the "green" stage, i.e. when it is dry to the touch, but still a little rubbery. You can wait longer, but as the epoxy gets harder everything is more difficult to cut.
Here I am using a jack knife, but a utility knife with a sharp new blade also works very well. Slice into the cloth tight up against the edge of the wood strip. Hold the edge of the blade against to the wood so you get as clean a trim on the first go as possible. Cut by smoothly and evenly pulling the blade along the edge. If your blade is sharp the glass will cut easily.
Avoid the inclination to "saw" at the edge. This will not make it any easier and your cut will be more ragged and it will take longer. If you are having trouble cutting cleanly, try pulling a little tension into the cloth.
After the initial trim, I flipped the boat over and cleaned up the edge a bit. I probably would have gotten a cleaner initial cut if I had flipped the boat first. Instead I used my knife to remove the biggest ragged edges. I then took a couple passes with a rabbet plane to remove the remaining edge of glass, making it flush with the wood.