I plugged in my phone and was trying to find how to download pictures onto my computer, so I moved my mouse to the right of the screen and clicked devices. It was then saying about second monitors, so I clicked it, wondering what it would do. Now, when I move my mouse to the right, it doesn't stop at the edge of the screen, I carries on even though I can't see it, as though I have a second monitor connected to it. How do I turn this off?