It is very easy to straighten distorted torn fabric. Hold it up and you will see it is a trapezoid. Get a grip on both short ends and give it a good tug along the bias. It will now be a true rectangle. The fabric is distorted due to the processes at the factory, so if you get a cut your grain is always off just a bit. If you fold your fabric selvage to selvage and then once more you will have a bit of of fabric nonaligned along the cut ends when you get it to lay flat, that is due to being cut off grain.