You must measure thru the center of the quilt top to bottom and cut the two side borders exactly then sew them on making sure they fit top, middle and bottom. Measure again across quilt including the borders you just sewed on, cut two borders, sew on top and bottom. This insures you will not have wavy borders. Wavy borders come from stretching fabric or not having the same tension on the top fabric as you have on the bottom. You should be able to gently lay the border on the bottom fabric smooth it and sew it so it fits evenly end to end. Pin it the first few times till you get the feel of it. Good luck.