A. Hopefully, you can slowly purchase more Mezuzot. (Remember, the cover is mostly for show, and makes the Mitzvah pretty, but the main thing is the handwritten scroll inside). For now, start with the main entrance door. This is providing that all occupants are obligated in a Mezuzah. But if you share a dorm-suite or apartment with someone who is not obligated (if they aren’t Jewish) then put the one Mezuzah on your bedroom door.