Borders do tend to grow and get very friendly (wave at you) if not done correctly.

The wrong way: This is how not to put a border on your quilt. Cut your border longer than what you need it and just start sewing from one end to the other and cut off the extra when you get done. This doesn't work well because the quilt top will tend to stretch on the edges and it will make the border bigger than the middle - especially if you have several borders on the outside of the quilt. Please don't do it this way - I have had to take pleats and tucks in borders and that isn't always a good solution.

The Correct way: This is the correct way to add borders on your quilt. This is assuming that you are going to put the side borders on first then top and bottom borders.

Step 1: Measure your quilt top to bottom thru the middle (sometimes it is a good idea to measure a couple of different areas and average the measurement).

Step 2: Cut the side borders to this measurement and divide it into 4th and mark with pins, also mark the quilt top in 4th with pins.

Step 3: Place the border face down on the quilt matching edges and pins - you may need to ease a little or stretch a little but shouldn't have to do too much if you were careful with your piecing.

Step 4: Sew seam and press toward border.

Step 5: Measure your quilt as you did above only side to side.

Step 6: Cut the top and bottom borders and follow the above steps to mark and attach them to the quilt top.

This will give you a very nice square, flat border.