At the bow I think I can get the halves aligned to within about 6" of end. At the stern, I don't think I'll be able to get them aligned any closer than about 18" from the end.

Make a curved test panel. Glass both sides. Try to compress it as you'd like to do with your deck ends.

Remove the inside glass with a heat gun. Try compressing it again. You'll find with one layer of glass removed the panel is quite flexible.

If this were my problem I'd remove the glass on the inside of the deck near the stems with a heat gun. THEN clamp the deck areas near the stems to bring them into the correct dimensions and apply new glass on the underside of the deck.

If you use force to join the deck and hull as it is now, this force will come back to haunt you when it gets released later and shows up as stressed glass with white dots where the epoxy is torn from the glass.