When you measure for your borders, make sure you measure through the center of the quilt, not down the sides, to allow for any stretching that has occurs. You can then ease in any stretch as you add your borders. I always pin on my borders before sewing to make sure I work in any stretch evenly. Once the borders are added, before I square up, sandwich and quilt, I stitch around the outside edge of my quilt top with a straight stitch to prevent any stretching. I stitch just under 1/4 inch from the edge so that the stitching will either be cut off during the squaring process or hidden by the binding.