First of all your center is just lovely. I too am working on a MC quilt. When I saw your center and saw that you need to make it king size I thought to take your center square and set it on point then surround it with a border of something. I used Flying geese in mine and it looks great and doesn't take away from the center compass. A long sawtooth would look good too.
Then I made additional MC blocks and set them into the four corner triangles of the quilt to get it back to being a square with the large on point compass unit in the center. You could enlarge those corner compasses by putting a ring of points or geese around them. By now you should have a roughly queen size quilt top which doesn't have borders yet. You can do more partial compasses to make up your border. This is what I am doing with mine. You can also repeat that border motif you used around your center compass.