Warming it in the sun may help. It's certainly worth a try.
I just replaced to top on my Toyota MR2 Spyder. It was the tightest top I've ever installed--seemed like there was no chance of it stretching enough to close. When I finally got it closed, I left the car in the sun for a couple weeks, and it closed fairly easily after that. Vinyl--even the fabric-reinforced stuff used for tops and tonneaus, stretches more than you might imagine.
Also--I've been told that professional top shops have steamers that they use to heat tops and get them to fit. Worst case, that might be an option.