Sounds like you let the ends spin when you pushed them together and loosened the spring even more. It works similar to a venetian blind.
The plastic end cover keeps it from unwinding when installed in the Jeep, as the ends are always depressed.
With it removed from the Jeep, push the ends together to release the latch, hold the ends so they don't spin, then wind the cover around to increase the tension. When the tension is correct, reinstall the plastic end cover. Then put it back in the Jeep.
It may also work to fold the back seats down, then wind it up in place (with the plastic cover removed). Just winding the cover around isn't enough. Pull the cover out and wind it around some more to put tension on the spring. DO NOT wind it too tight or the spring might break when the cover is pulled all the way out. If it feels like it comes to a stop without coming out far enough, don't force it, you have the spring too tight. Just wind/unwind the cover until you get proper tension AND enough length when the hatch is open. Then reinstall the plastic cover.
