I was messing with a zipper today which I wanted to sew in for my tarp tent (sorry I really wanted to make one, don't hate me). I am using it for the door and I see how people make the zipper turn to zip parallel to the ground then up the side of the tent. How do you make the zipper curve like this? When I was playing with my zipper it didn't seem to want to be bent without starting to fold up. Any help would be appreciated. Thanks.