Originally Posted by Jan in VA
Turn your current design on point, let it "float" so the current borders do not quite touch the new borders, use blocks in the corners made with what remaining fabric you have - perhaps in the same "compass-type" design, and add finishing strips and triangles around them. Then if you wish you could add wider borders on top and bottom to make the quilt rectangular instead of square.
Jan in VA
To make it float, turn the quilt on point, add corners by making a block and adding half square triangles to each side of it to make a large triangle to add to each side of the quilt. Then put a sashing around each side that matches the color of the half square triangles. Then add a darker border to contain the quilt.