I actually just changed the momentum physics. Should be more intuitive now. You keep momentum by holding forward instead of letting go of directions.
I agree that if I want to keep the larger levels I need to fix the amount of backtracking you need to do if you die. Definitely on my to-do list.
Collectibles not counting seems worrying. It worked perfectly fine during testing. Did you die after collecting the other three? They only get counted if you survive until the exit currently, once again, bit of a bad system.