Moving/floating desktop

Linux was working fine and I was getting the hang of it, then I obviously did something wrong because now when I move the cursor the desktop background moves too, a couple of inches in any direction that I move the cursor, as if the desktop is too big to fit on screen and therefore moves around in order to fit. I tried a "roll-back" and although I have several roll-backs on file I can't figure out how to apply them or 'mount' them as I believe it's called. (I can't figure out a lot of the jargon)