Thanks for the pictures, I can believe you would have difficulty getting the gunwale to take the plans shape by just bending it in one plane. Looks like if you attached the gunwale to the center frame first, the bow at least would have been 2-3 inches low. So then you would have to bend it up, but when you turned loose of the frames that bend would try to straighten out causing the midships section to pull up.

I think the only way you would get that to stay in the designed arc would be to steam the gunwale and hold it in position while it cooled. The alternative would be to split the 3 pieces along the length and then laminate them in position to match the gunwale shape defined by the frames. You would still have some springback but it would probably be very acceptable.

That way you would not have the hogged keel.

I had a similar problem (hogged keel) on a stitch and glue kit. Caused by me not following all the directions. That boat would go straight ahead, but would not turn at all.

Marc