If you cut your strip at 2 1/4 ", fold and place it even with the edge of the fabric, and sew a 3/8" seam allowance, the fold will just meet the seam after you fold it over the edge of the quilt sandwich. You aren't allowing anything for the thickness of the quilt (batting and two layers of fabric) or for the fold to cover the seam. You could make the seam allowance a little smaller, or cut the strip a little wider, and it will be easier to turn.