Start with the center heart when you are ready to adhere the hearts to the backing fabric. Remove the paper backing of the WonderUnder and iron the first heart into place. Repeat with the hearts on the left and right of center, and then finish with the final two hearts.
After hearts are stitched down, it's time to stitch the 'string' the hearts are 'hanging from.' I used 2 strands of some dark gray DMC floss and backstitched along the line I'd drawn on the fabric.
When you get to the edge of the heart come up inside the heart about 3/4" from the edge, make a 1/2" stitch" and resume stitching on the other side of the heart, so it looks like the hearts are threaded onto a string, hanging like a banner.