Install the hatch hinge with the hatch on and tight. Before you hang the hinge the hatch will already be aligned and supported by the ledge.
Do this without the tear roof over the galley on.
I have the roof fabric run right over the hinge, however my hinge is attached to the aft face of the aft spar, and the top face of the hatch spar. It is 90 degrees when shut, and straight when open.