I guessed wrong

Because of the huge arch in the flounce you will need to purchase a yard of the separate contrasting fabric or live, learn, and make do as I did and piece your flounce together like this:

1. Cut out what you can so you know what you need.

2. Allowing for a 5/8inch overlap, pin and cut the added fabric.

3. Pin in place and sew pieces together using a 5/8 inch seam allowance.

4. Press seam open.

Together at last, together forever. After pressing you can hardly tell it was pieced together. I really lucked out with the fabric design.

If you want enough fabric to make all your straps and flounce in the contrasting fabric you will need about a yard and a half. Then only buy 1 yard of the main body fabric.