I got 2 broken ones. One looks like it will work but it is 4 inches short from side to side and won't let me install it in the back. The other doesn't want to roll back up on its own.

 

I fixed mine some years ago,So this may work for you, but its a little hard to explain.Anyway,If you roll out the cover,then continue to rotate the bar past the point it stops(you'll have to somehow fold the edge of the cover around the plastic end caps as you rotate it).At the same time someone has to hold the ends from rotating.Only the bar should rotate with the cover.Do about 5-7 revolutions.As you complete a turn check to see if the bar wants to turn backwards(or roll up).If you've done enough revolutions the cover will rotate all the way back.If not try a few more revs.This work for me, but only after 2-3 trys.So far though my cover still works fine after 3+ years.Good luck.