You can also cut it in half and reglue, if you're careful it will hardly show, then plane flat. Is it finished? If not you could try the lawn trick, place it out in the sun on some grass convex side up, and wait see what happens. It has worked for me, but with panels that have cupped. Keep an eye on it if you do this, sometimes it starts moving quite fast. Once it's straight get it back inside and finish as soon as possible. Another solution, if I understand the situation correctly, would be to just turn it upside-down so the gap doesn't show anymore?
Frank D.