When I used them for an appliqué I did last year, I had the same question. What I came up with was to make a template out of heat resistant plastic half the size of the circle minus 1/4"(you will have to make a sample circle to use with yours depending on how wide your turn under is), stitch around the edge of the circle as directed, insert the disc into the yo yo before I drew it up, and starched and pressed it, let the thread lose, remove the disc, then tightened the thread and tied it. That gave me a nice smooth edge to blind stitch down by hand, with the gathered side out. I did use elmers glue to hold them in place until they were stitched. I hope this gives you some inspiration for your project.