This is a really cool concept but boiling it down to a simple jumpscare is a rather underwhelming note to end it on, considering how much you could make the player paranoid about something being behind them without resorting for the most extreme option (the door opens and a monster enters) right off the bat [a greater focus on ambience would a long way for freaking the player out, espec. considering that all the scariest moments I've had in horror games *have* been from the ambience, and the times you lose track of whether a sound effect is simply coming from the game or if it's coming from real life]
that or taking the alternate approach and messing with the player's own reflections, the way staring at a mirror with little to no light gradually morphs your face into a form worse and worse the longer you stare (considering how much uncanny valley already plays into horror you could exploit this a ton by applying it to the player's own face)
Either way this is a super interesting experiment and -- if you ever feel like expanding it -- I'd love to see more of it