I am making what will be a diagonal set quilt top for a twin bed. It's 8 inch lemoyne squares set 7x7 - 7 across and 7 down. How do I figure out how to square up the sides so it will finish as a square with a diagonal center? I think I need some math instructions here. It measure roughly 77 inches point to point and the sides are 56 inches long. Any help will be appreciated. Thanks.