Are you trying it with the roof in the protective bag, or "nekkid"?
Believe it or not, a local S4s owner here had a factory roof bag that was so thick it prevented the top panel from fitting into the boot.
It's that tight.
You may need to insert the panel into the bag "backwards", that is, either upside down from the way you are trying, or with the opposite side leading.
That way the seams will end up in a different area and hopefully you will be successful. :bow:
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PS, The hacksaw was used by the factory. -eek- I saw a restored Investor Edition G-car (the first with a removable roof, IIRC) that had notches cut into the boot openings. The owner said they were Factory. :up: