You described my rug exactly! Tsunami waves of is!

Onebyone- going round and round with it can be boring. Mine had tons of waves and the instructor took the best press and a hot dry iron and did her magic and made it lay flat. I mixed a good quality jelly roll with a not so good jelly roll. The instructor blaimed the cheap fabric for the waves. We all kept saying, well, it's just a rug!

I did use the Katahdin batting strips and a Robert Kauffman jelly roll. My rug sewed up flat. I don't know if this made a difference or not. I did not press it at all.