Do you remember if the border distortion was there before quilting?

Yes it was. I've since followed the advice given above: cutting the border strips along the lengthwise grain, and measuring the strips and cutting them to the middle dimensions. These worked perfectly and there was no distortion in my latest quilt. I love this list! I think I could cut across the WOF if I starch the fabric first--it would serve the same purpose of avoiding stretching.