Mountainless world

So first I want to say thanks for the tool, of course. It's amazing and it saves a lot of me amateurishly fumbling around with climate generation and such, and being able to import my bar-napkin map is phenomenal! I wish I had started with this.

That said - I imported my map and tried all sorts of things to try and get a more natural-feeling world, or at least less human-crafted... And no matter how much I randomize and mess with the heightmaps my entire map is pretty samey and flat. And I have seen not even a single mountain or valley - just endless plains. Am I messing up somewhere or missing something? Could it just be my world is too small? I've pored over the wiki but haven't found much on it.