I made several OBW's and didn't find the fabric-stacking to be that hard. If it's off by just a little it won't be noticeable in the finished product. It's recommended that you not wash your fabric first. I am a pre-washer, but when I buy fabric that I think I will use in a S&W or OBW I make sure not to wash it. I am sure you will have no problems. Be sure to post your finished quilt.