There is this really annoying glitch that would happen to me on my laptop whenever I had it on standby, unplugged it from the charger and then left standby. What would happen is the screen would have less width than it usually does. So over the months I had my laptop I figured out too ways to fix it. Both really simple, but you have to do them every time the glitch happens.
|Sorry for the bad quality|
So the first method is the easier one. Just press Fn+F7 to switch the projector mode. Depending on your laptop you could have a different hotkey. Alternatively you could search using the spotlight for 'Connect to a Projector'. Just choose 'Computer only' and the screen will go back to normal. Dead easy!
The second method is a bit longer to do. Right click on the desktop and choose 'Screen Resolution'. Near the top right of the window you'll find a 'Detect' button. Hit that and you're ready to role!
So that's pretty much it. Have you got any other ways to get the screen size back to normal?