Don't worry and don't cut up your 6 1/2" squares. If you sew two of the 3 1/2" x 6 1/2" together, you will get a finished four patch that is 6 1/2" square to alternate with the focus fabric 6 1/2" provided squares. The math may seem off but you do need that extra half inch for your seam allowance. I make crib quilts using these measurements all the time and it does work. Just go ahead and make your four patches, stitck a 6 1/2" square in between and you'll have a completed quilt top in no time. Happy stitching!