Before attaching borders, carefully press the quilt and border pieces. The borders should first be cut a few inches longer than you think you need, then trimmed to exact length. To trim your side borders to the correct length before sewing to the quilt, lay out the quilt on a table or carpet. Pat it out as flat as possible without stretching or distorting. Lay the two side border pieces along the quilt's center line (top to bottom) and pat them out flat. Cut the borders even with the top and bottom of the quilt body.
Mark the center of each quilt side and the center of each side border. Pin the ends and centers together. Add more pins, carefully working in any fullness with pins. Pin every 3 to 4 inches. Sew with the side that has the most piecing down. Press.
Do the same thing with the top and bottom borders, but remember that the quilt is wider now. When you cut the top and bottom border pieces to their first approximate length, be sure to measure across the quilt, including the two side borders (and add a few inches). Lay the borders across the center of the quilt (side to side). Trim the borders as before. If you follow these directions, your quilt top will be a perfect square or rectangle and will lay flat!