I feel like I've searched the entire house and seem to only be able to find the shelf near where you need to install it and the one upstairs, cannot find the last one however... Anyone know where it is?

to answer your question directly, most likely you're missing the shelf in room 204. but if you need more help, your best bet is to hit up the discord channel for these types of questions: discord: https://discordapp.com/invite/nH42eyQ