I use to be partners in a quilt shop and we always tear the fabric. This is so there is no waste and things are true. When you see that angle at the end of the fabric it is caused by the way they put the fabric on the bolts at the factory or the distributor. It is twisted a bit. If you are luck enough to have a long or mid arm, you can attach the torn ends and roll it back and forth adding a bit of tension and straighten the longest of pieces lickety split. Wide backs are impossible to cut straight rolling will fix them up pronto. If you don't believe in washing first, use this time to spritz your fabric with a bit of water and a little bit of fabric softener as you roll. Smooth the fabric on the pick up roller and let it set for about 20 or 30 minutes. No need to iron.