I think I would either change the number of outside triangles, increasing them so they form more of a straight line at the corners, or increase the width of the border so that the triangles are right angle triangles. I've attached a few drawings to show you what I mean and I included one that uses HSTs in the corners for a different look.
If you stay with your current designs, I would print out a template, since you'll only need to print one. With paper piecing you'd have a lot more to print, or print then trace.