I think pictures would certainly help get a better idea about your concerns.
There will obviously be a little bit of a gap around the edges, assuming for the kerf and sanding afterwards. And I’ve seen varying degrees of gaps across builds.
I doubt the hatch would flatten out, but I suppose anything is possible. I left mine sitting ‘vertically’ for over a month with the front edge (end with the stiffeners) on the ground and had no issues.
FWIW, I had concerns about mine as well, but minus one mistake (on my part), the galley hatch on mine fit well enough with ‘minor’ adjustments.
-Adam