Single click places an x instead of a sunflower. I solved the puzzle but placed those xes instead of sunflowers and was confused why it doesn't say I solved it. I would suggest making a single click be the main action, ie placing a sunflower.
It would be far too easy to accidentally tap the screen and burn a Mistake, and if its your last one that would be frustrating.
This is how most of Simon Tatham’s puzzles work, and that works well.
They btw also have a feature that swaps main and secondary action when toggled, which could work here.
2. Even if brute force was a viable option for solving, an easy fix is to have a “submit” button when you think you’ve solved it (and that can track strikes for invalid submissions).