Is your binding straight of grain or bias? I found since doing my binding with a straight grain that my edges lay flatter. It's seems that the bias binding stretches either the quilt or the binding and I get ripples no matter how carefully I sew it on. I only use bias for doing scallops or curves.
It also helps if you can cut the long side borders down the length of your yardage. It does take more material to get the border without seams but there is less stretch down the fabric length. As others have mentioned, you can block your finished quilt to help your wavy edge.