OK....I have two pieces of fabric....one is a panel measures at 39" x 32". I want to use the second piece of fabric measuring at 47" x 42" as the backing, and by sewing it the Jenny Doan method, sewing the right sides together, the sides first, then the top and the bottom,( leaving the little opening for "birthing"), then cutting the corners at 45* angles, and then birthing, has made NOT flat borders for me. I can't even explain what it made, but I guess the best way to say it is that yes, they're mitered but not flat. Forgive my ignorance.