Originally Posted by feline fanatic

One thing I have not seen anyone mention... By the look of the picture you are on the very edge of the quilt out in your border area. Did you measure your quilt through the center and then cut your border to that measurement? Or did you have a long strip of prepared border (even pieced) that you sewed to the edge of your quilt then cut off once you reached the edge?
If the latter, this method often results in wavy borders with excess fabric. The excess has no place to go and often results in pleats like you pictured. Your pleat almost looks like that is what may be contributing to your problem.