Originally Posted by
Barb_MO
After sewing two diamond segments together and press the use a ruler and make sure that the square at the points, if it doesn't readjust your seams and check again. Something people will want to trim it up, but then the diamond points will not be the same size. Same goes when sewing the two pairs together, put a straight edge all the center part and make sure it is straight. When all sections are sewn together you would want to press the seams to all go in one direction, open the center points and take out a few stitches and you can get the center seam allowance to swirl and it should lay flat when pressed with the swirl.
I think Barb has your answer. Trim and square
every seam as you go. There are diagonal lines on the ruler. Use them and make your edges match. When you get to sewing the last two halves together, both edges must be straight.
Pressing all seams the same direction around the center makes it much easier to sew onto the next portion. I always try to have the centers to my right, wrong side up, and press away from me. Then turn it right side up to be sure all seams have no creases and are nice and crisp. When finished, you should be able to run your iron all around the center on the wrong side in a clockwise manner.