Ok so, I'm already stuck in the 1st room trying to find the key that the voice supposedly left for me (can't find it for the life of me) and while exploring I accidentally found a way to go out of bound.
on the right where you entered, there's 2 barrels and a metal shelves. you could jump on top of the barrels, and then on the shelves, and then on the thin wall to go out of bound. it's not the intended way but it's the only way I can find that lets me continue without trying to find the impossibly small key in the dark room... where ever that key may be
Edit:
just completed the demo, the combat feels a bit slow and there was a time where an enemy was somehow able to hit me despite they already in the dying animation. The key finding in the beginning after you get the gun was also annoying as the game is super dark, your aim needs to be specific to get it, and there's no hint where the key is; I think it would be better if there's maybe a little shiny hint of objects that you can take, or alternatively increasing the hit box of the object.
Beside that, the game's atmosphere is pretty good and I like the art style it has, kinda doom-like. maybe make the game slightly brighter (or add settings to increase brightness) that would be great. I love to see this continue if there's a change to the feel of combat (if you want it to be slow then reduce the enemies you fight, if you want it to be fast decrease the cooldown of each hit)