Originally Posted by
Mkotch
I was also careful not to stretch the binding as I sewed it on.
This might be the problem. If you added a bit more binding than necessary in your caution not to stretch it, the excess would cause the ripples. On a baby quilt, as little as 1/4 to 1/2" extra binding on a side will be enough to make the edges wavy.
I would try dampening it and pinning it flat as QuiltnNan suggested, but if that doesn't work, removing the binding and redoing it would be my suggestion, this time not worrying about stretching the binding.
Edited to add: a picture might help determine if the issue is quilting density or something else.