Welcome to the pain in the butt, class of winshield builders. I HATE to do them. They are so time consuming. I am going to try Doll House window frame strips. They have a mitered groove for clear stuff. Will try straight Amonnia to soften the strips.Shape it with clamps, dry, washout the Amonnia while still clamped, dry. Put the plastic windshield in. Not sure what rewetted Amonia would do to plastics.

Rich