You might have already gotten this, but basically the map has something in it's layout that doesn't match with the layout you've seen as you walked around. Check the bottom right of the map.
(full SPOILER answer)
The bottom right of the map shows a long corridor-like space in the basement in the room with the closet (below the laundry room). If you go in that corner and interact with it, you will be told there's a vent that is screwed into the wall. You need the screwdriver to open it and get in.