To be clear, I liked the design in general, and I did notice the elements you were progressively working up. I was indeed using the letters, I just hit a big stumbling point in one spot. I think a simple fix would have been to not start the player from all the way back at the beginning of the level when they fail, but maybe just rewind a little bit back. I'm pretty sure that alone would have resolved the problem for me.
I really did like it in general.