Fabric is put on bolts by machine. Many times, than not, it gets pulled to one side in the roll process.
A Home Ec teacher always made up straighten our fabric prior to cutting. Sometimes it was way off grain.....We worked in teams. We were taught to pull a thread to get the real true grain. I DON'T DO THAT ANYMORE...WASTE OF TIME. But I do smooth out my fabric, then line up the pattern so it is straight, then I get my husband on one end of the fabric piece. Open it up to the 44/45 width, like you are going to fold a sheet. I get my husband to pull hard on the corner that is not matching up, while I pull on the opposite side. This works against the out of shape,pulled portion of the piece. Basically you are pulling it back into shape. You have to do this several times to get the pattern in the fabric to even out.
D inTX