Yeah, these kinds of undulations are frequently a problem when you try to use a larger number of sections.

It's annoying because you want to add more sections to create more control, but since the surface is forced to go through each section there is sort of a "ripple" effect that happens.

You may try to use a fewer number of sections.

Another thing you can try is using loft, with the Loft Style = "Loose" - this will make a surface that is just guided more gently by the cross sections instead of being forced to go right through them, it tends to build a more gentle surface.

If you can post the .3dm file, it could help in suggesting some tweaks to make it better.

- Michael