I measure my quilt longways through the center and cut the side borders the exact measurement (sometimes they may have to be pieced together). I find the center of the side of the quilt and the center of the border and pin the center points together. Then I start sewing them together with the border fabric closest to the feed dogs, easing if necessary. After pressing the long seam to the border, I measure the center and add the top and bottom borders in the same manner and press toward the border. Good luck with your quilt!