I had the same problem but just layed the outer edge strip on it's side and then planed the pround edge off when I joined it on the deck. I had built a full size one before and knew this challenge was coming. When I built a 15'5" GA I leveled off the hump on the back deck a bit. This lowered the volume a tiny bit, but it was a day paddler anyway. I also made sure the shear strip and the 1st deck strip were cut from the same board next to each other when I cut the strips. Good luck and happy building!