Thank you for all the replies
Well, I went to the feed store yesterday to get alfalfa cubes since those bags can be loaded in thru the side doors or strapped to the roof. I told the guys at the feedstore about my situation with the sheet stuck in the hook-latch-thing, and between the two of them they were able to get it out by having one person pull on it from the inside and the other try to open it from the outside (a suggestion from you guys, lol) and it opened!
So now I can continue hauling hay and making a mess in my car!
All I need now is to get my truck fixed before I have completely transformed a perfectly nice car into a beat-up hay wagon