Dig thru your pile of cut offs or scraps and find the piece that matches. Cut a wedge shaped piece to fit in. Wet the boat and scrap to make sure it matches . Don't throw away cutoffs until you have faired hull out and filled if needed.Light wood really does show any gaps. Your gap may benefit from a wet spray and single edge razor blade removal of the glue bridging the gap, otherwise the wedge will not fit in. Give the water time to turn the glue white again before slicing it out of gap. Try to not make the gap bigger with the blade. Resin that fills in during laminating will be walnut dark. rh