Stunning, Tallchick. You've got points coming off your points. Where are you going to put the first border? I agree with stay stitching or running a chalk line. If that were mine and I got it anywhere near a sewing machine it would soon have 5 sides. I'd like to see a picture of what it is supposed to be.
I've got two books on borders and neither one has something that complicated in it.
Marcia