I didn't install a forward hatch so I am pretty familiar with the problem of aligning and fastening an s&g hull-deck seam with limited or no internal access.

When that happened to me I used knife blades, tape, web tie down straps around the hull, anything neccessary to force the joint into alignment. And then I drilled a new hole that passed through both the deck and hull panel- this automatically aligns the holes so the wire can pass through both holes and then be tightened. Of course this only works near the bow and stern, where the hull-deck joint is closer to a right angle.

Next yak I plan make extensive use of CA glue (super glue) and accelerator when fitting and aligning panels. I hope to use 3m blue tape instead of wire but expect a few places where only wire will suffice.