What I do, is bring both my sides of the quilt together...then measure the lenght of each side and on the fold end I would measure...generally, if the two side borders are so closely matched in measurement I will use that (Left border 68 3/4", right border 68 3/4 and a little bit, folded edge 68 1/2" (which would be the center of the quilt)I would use the 68 3/4 in...mark the center of the border strip and middle of quilt...match the center marks up and pin, then gentle flatten out my border strip one way to corner and pin...if there is a little over hang, I leave it until I have the border completely pinned on...then if you trim off the border strip, make sure you trim it at a true 90 degree angle...hope this helps...