I wonder, too, if your fabric is not folded correctly BEFORE cutting. If you are a pre-washer (as am I), then you need to make sure your fabric is folded on-grain vs just in half, selvage to selvage. Start with your fabric folded selvage to selvage. You will likely see a 'bubble' in the fabric at that point. I lay mine flat on my pressing surface and then smooth from the fold line toward the selvage and outside edges. You'll likely lose some fabric when making that initial straightening cut but your fabric will behave better throughout your project if you go through this process. Just a suggestion.