I’m past this point in my build, but if I would have thought about it before I added the galley flat, I would have added a strip or two of fiberglass to the bottom section of the galley hatch beforehand. I did this to the doors before I cut them out, and I don’t seem to have any spring-back on them after they were cut out. As it is, the galley hatch only has fiberglass reinforcement on the top side, which puts it under tension to curl up, with no countertension on the underside to hold it in place. Adding the fiberglass on the underside would provide this countertension and make it more likely to hold its shape. I may still do this before I finish the underside, possibly slightly pre-tensioning it with a clamp to ensure the outside edges mate first just before the center.