Jo, your post is the most beneficial personally to me so far. I can visualize your procedure. I have a few questions for you:
Did you put the "right side" of the backing fabric so that it could be seen between the yoyo's or turned so that the right side was seen on the back side, like a regular quilt would have it? If you had the right side peeking through the yoyo's, did you use a French seam when piecing the backing?
Also, I think it would be difficult for me to do that hem after the backing was attached to the yoyo's. Did you perhaps attach the yoyo's except for maybe 6" all around, then do the hem, and finally attach the last of the yoyo's all around?
Before attaching the yoyo's, did you pin each one to the backing?
Did you use any kind of hoop when sewing down the yoyo's?
Thank you so much for posting. In addition to the technique, you have given me the courage to forge ahead!