Thank you for such a detailed comment! The block that's still there is where I am considering adding more levels in the future, but right now it's just there.
I'm not totally sure how I would go about making a back button but that's a good idea and I will see if I can make something work.
Unfortunately, ESDF is built in to PICO-8 so I can't change that.
I'm really glad you enjoyed the game!