Hey Sara, I'm so sorry! It looks like there's only one combination that lets you make clay (and therefore clay pots, and then flowers), and you need water for it... and there's no water for that level 3a. I'm gonna fix this and put out an update right away. So sorry we didn't playtest enough to catch this.
We'll work on making some more intuitive combinations to get to flowers in different ways, and we'll definitely be adding more hints early on to make the learning curve a lot smoother.