Pick your repeat spot, the tip of a leaf etc. on the selvage side of the fabric. Find that same tip of the leaf on the other side of the FOLD and stick a pin in. Take a long ruler or square and make sure the repeat is running straight on the grain, if not you may need to cut the fabric. I had this problem when I wanted to do my 4PP. The fabric was off about an inch but I managed to cut 3 of my 4 stack of squares and then had to readjust my stack. Hope you have better luck.