Windshield gasket

[twoskies]

Morning

Got a 66 c10. That I’ve replaced the inner roof and the outer front upper panel
I replaced the inner roof first. Leaving the outer front panel in place for reference
Then when I was ok with the fit. Welded the inner roof in place
Then with the inner roof stable.
Cut and replaced the front outer roof section in
I want to be sure I have not changed the pinch seam
I’m trying to put a windshield in to check. New gasket
Here’s the problem
I can’t get the gasket to start I’ve watched several videos. Some use glass cleaner some use soapy water some use nothing
Including two pictures. Assuming the small opening goes to windshield bigger goes to outer around the frame. Makes sense
I’ve left outside in driveway for a few hours. No difference
Might try a heat gun

Thanks for any help