Hello,
Thank you for your comment and kind words.
I'm glad that you saw the search for the key as it was intended, as an opportunity to explore and not as a torment because you have no way of knowing where the key is.
I listened to your advice and in the final build, I added more checkpoints for that level. Also, I've added a "How to play" button in the main menu explaining controls and the goal of the game, so you don't have to figure out by yourself that you can sprint(sry about that :D).
Thank you for your advice!