I would go back up to your post about "adding another border" The quilt should be squared up before you quilt and bind. Perhaps I am not understanding the sequence here. Have you quilted it? If you have then most likely you can't ad another border. So If it is quilted then trim and measure and try to do the squaring with the binding. Am I really confused here about the stage you are in? You don't say how much the sides and ends are "off" Are you binding with bias or straight fabric? If it is quilted then measure and put pin the bnding so each side will be the same as welll as the ends. Your binding will have to scrunch in the difference. The borders should have been used to assure the quilt top was squared before quilting.