Include your email address to get a message when this question is answered. Trim your threads and any seam allowances that cause bulk or stick out from the elastic, then fold your elastic to the inside and stitch your second pass of zig-zags. Draw diagonal lines from the top corners to the top of your middle line and diagonal lines from the bottom corners to the bottom of your middle line. Leave the shorter sides, which will eventually go around your waist, open. When I made these my elastic flips over to the right side when wearing. I do have a previous tutorial I did back when I was still experimenting, which may help, but I have it down to a science now!
Tie the tops of your straps together behind your neck and the bottoms together behind your upper back.
Watson Sew Along #7: Cutting & Sewing the Bikini