I stop sewing and take a backstitch at each point that is supposed to be in the center except for the final one where you sew the halves together and then I press that seam open. If the fabric is extra thick, I'll press the east/west seams open also. I have pounded denim with a hammer to flatten out seams so it should work on cotton also. I didn't use a rubber hammer--I used the real deal carpenter's hammer.