You can do a diagonal seam, and the only thing you need to remember is that the two ends should overlap by how wide your binding is. In other words, if you cut your binding 2.5" wide, then have the ends overlap by 2.5". If you cut it 3", then the ends should overlap 3". After you cut the ends, turn them 90 degrees, stitch the diagonal seam, and you're good to go.