This really does feel like a horror game. It looks like you already spent a lot of time on it - the atmosphere is great. I liked that every action has sound feedback, from footsteps to interactions. That adds a lot to the immersion.
I think it could also be cool to place the mansion itself in the main menu scene, so the player immediately gets a better sense of the location before starting the game.
I also liked your approach of replacing the standard UI with handwritten notes. It feels much more authentic and fits the horror style well