Just a little more details here. I am a woodworking, so I am familiar with wood movement due to moisture. I don't think that was what happened.

I had glassed the top on the form, 3-4 days before. I had removed the top and done some work on the hull. Few minor things left to do before jointing the two. Had sat it back on the hull a few times so there was no problem with the fit. A minor amount of movement but nothing that hand pressure wouldn't pull down in place.

Move it outside. Disk sanding the underside of the hull. Knocking down any high spots and glue squeeze out. Moved it inside and glassed and epoxied it. 12 hours or so latter I discovered it had curled up. It will come back down but it is going to take some serious pressure with some straps. Hand pressure will not longer flatten it out. I need to try out a couple of things but I think I am going to have to clamp it in place and then run tape along the outside edge between the straps. I don't see just putting epoxy on the sheer clamps and ever being able to get that deck in place and shape without a huge mess. The ends where it was mostly flat I can, but not around the cockpit.

Speaking of which I am thinking of opening up the small hole I left for the cockpit. Not full size opening yet, but that should relieve some of the stress at the back bulkhead and make it easier to flatten that section.

Next time I think I will just coat the inside and not glass it. Be ready to put it on hull just as soon as I the epoxy starts to set up too. Probably didn't need the glass but I just wasn't sure and didn't want to regret it latter.