Rather than cut a straight sided strip, and then have to bend it to fit the curvature of the boat, try this.
Clamp on a piece (or several if you have to) of plywood to the gunnel. Draw a pencil line on the plywood, along the top edge of the gunnel. Cut it off to fit.
Rather than have the joint in the center, I used a long piece in the center and two short pieces on the ends. That offsets the joints for a bit more strength.