You can add cross beams to the underside that are the correct curvature to match your deck.

I would grab a piece of 1 x 2, 1/2 x 2, or some such that you have laying around, cut it slightly shorter than the width of your hatch opening and mark the curve of the deck onto it. Cut the curve in it and coat it with epoxy then glue it to your hatch lid, forcing the lid to match the correct curve.

It all sounds easier than it actually is. Matching the curve and then keeping the hatch bent while the epoxy dries is a little tricky but doable. I've had to do this on one of my 2 boats.

Good luck!

Ben Staley

: I am completing the Gillemot Great Auk. I cut out the flush hatchs and
: intalled the fiberglass lip and placed a foam gasket on the hatch to mate
: withn it. At this point, I discovered the fore hatch has sprung back (not
: now the shape of the deck). Is there a techniqe to bring this back to
: conform to the deck shape?