I had the same problem on a Grand Laker canoe this summer. The sides curled in almost 10 inches during a couple of blistering months of dry weather. I used a spray bottle and misted the inside for a couple of hours before beginning to ease the forms back into place. The moisture eventually caused the curl to relax to within almost 3 inches of the original shape. Reinstalling the forms didn't stress the shell as much that way. I left the forms in place for several weeks before doing any more work so that the inside was completely dried.

I still ended up with minimal separation along some of the strips from the pressure of the forms. Before I glassed the inside I filled the spots with epoxy and web clamped until set.

Now that it is done, there is no evidence of the this problem that I was sure had almost reduced my project to expensive kindling. Press on, it can be managed.