the easiest way to do an odd size panel is to either trim it to fit the 5" or 6" squares - or - make your squares, lay them out on top and sides. Place a 'special' print/embroidered square in the corner and see how big a strip you need to fill it out. Then add a very special piece of fabric (something that either ties in all the colors or the theme) to each side of each corner piece. This will probably be between a 1/2" to 1" strips. I would use this same fabric as my binding. It will all tie together. (Also, depending on your panel and the fabrics involved, you might even add a strip halfway down the side to plump it up.)The only other way is very math heavy and if you are math challenged, this could become very frustrating. good luck.