I have a piece of fabric that I needed to cut into a fairly large rectangle: 38.5 " x 57.5". I snipped into one selvage and tore across the WOF. Then I measured down to about 60" and snipped and tore again. Then I lined up the selvages to fold the fabric flat, and my tear lines were not at all lined up--at least an inch off. Why is that? Why wouldn't they be perfectly straight since the tear is on the straight-of-grain and so are the selvages?