After straightening the form the transom sometimes STILL have a bit of a twist to it. Run a wire from the top of
the stem to the far corner of the transom. Twist the wire until top edge of the transom sights straight and true with the top edges of the temporary ribs. Leave this wire in place while installing the bottom panel. Later, after flipping the boat over, leave that wire still in place until a rear seat, rear deck or rear dry storage locker is installed. That will hold it square thereafter.