I am a new quilter and did a McKenna Ryan 12 pattern applique quilt...lots of work. When putting the borders on, I just cut a long strip of the border fabric longer than the side and sewed it on. Well, there was NOTHING I could do to get the wave out but to remove the strip and measure it to the same as the other side to square it up. I will ALWAYS do it as AndiR recommends from now on. It was perfect after redoing it and has nothing to do with the quilt police...it just needs to be the same to lay flat. I suppose the larger sizes make the bigger difference. Thanks for the tips!!!