Termi ... I've had the waves happen with some of my yellow. I was blaming it on the fact that it was a batik. And too, have thought that perhaps the iron was too hot as it doesn't happen all the time and does not seem to be happening to my regular quilting cottons. I've started to use BP, but have NOT used it on the PC yet (trying to use up stash of spray starch). So I don't think it's the BP to blame .... and I have been able to get the waves pressed out, eventually.
Wonder? try a spritz of water, and then press those waves out?
Great fabric choices for both blocks. The subtlety of D+D works! And love the FUN in Elsie's! Your curves are more than perfect!