: Can you put a spreader stick in the hull to push out the flat spot?
: What boat are you wrestling with?
: In a perfect world everything fits but you will find that you can have a fair
: bit of wiggle room to get things to fit.

After I had stitched the hull, I used "pullers" instead of spreaders. That is, I wired 3 copper wires through the holes at the top edge in the flat area and ran some straps through them, which I attached to a weight on the window sill next to the hull. I tensioned the straps to pull out the flat spot to the desired width.

This method did help. I just should have used another 2 wires in the next holes down! The flat spot's length was reduced but there was still a little section left that was too flat.

The kayak is a Merganser 16.