Linux Mint: "Move to monitor 2": but I don't have a second monitor. How do I fix this?

I have a fresh install (about a week old) of Linux Mint 17.1 Rebecca (love the name!), Cinnamon edition on my laptop.

If I right click on a tab, I get the option "Move to monitor 2". The problem is that I don't have a monitor 2. Here's a screenshot.

Also oddly, if I take a screenshot, it shows two screens (one I'm unable to access). See below:

Q: How do I fix this? I only want one monitor (the laptop monitor).

There doesn't seem to be anything relevant in System Settings. I'm a new user (after switching from Ubuntu), so I might be missing something obvious.