Its been so long since I have replaced a top but I did just install a Bestop fabric camper top on my Tacoma and the sides were 1-1/2" short on the sides for the windows to zip in. I was working in my garage and it was 60 degrees. I got my infrared propane fish house heater and warmed the fabrid (be careful if you do this as the heat can destroy the top very quickly if your not careful). After it was thoroughly heated, I was able to get the zippers engaged. Now even when cold I can remove and install the zipped windows. So my guess is that it needs to be a bit warmer but I would call the manufacturer before you do anything rash...like listen to my advice or return it.
This is a Kee top. Just returned an EZ ON top for the same reason. Starting to think I’m the problem, not the tops! I have it sitting a few feet away from my pellet stove draped across stools now. Seeing a lot of talk about steaming online. My installer is a 2nd generation upholsterer and is scratching his head. Was hoping to get answers here, but I’m glad if my journey turns out to help others. I’ll keep you guys posted. Thx for all input guys. So you know… the Kee and Ez on are very similar quality however the ez on was a slightly brighter white if that matters to any restorers