Hi! Looking at your playthrough (thanks for doin' it by the way!) you didn't flip the circuit breaker, which spawns the key in one of the bathrooms. Looks like it's an error on my end, with the interact UI message not showing through after you pick up the note next to the circuit breaker - it's my bad!
If you want to play through the game again, just make sure you back off a little and get closer to the circuit breaker again - then you should be able to interact with it. Sorry about the issue! I won't be able to work on a fix for a few more days unfortunately, so this could be a way for you to see the ending still.