If you've got a full-size window on your screen I would expect F-F's solution to work. (If pressing Ctrl and Zero together doesn't work, try pressing Ctrl and + together until you get back to the normal size).
However if you've got a window which occupies only occupies part of the screen then you need to maximise it (by clicking on the little square at the top right of it).
If all else fails you can reset Chrome (although I'm confident that you shouldn't need to do so):
https://support.google.com/chrome/answer/3296214?hl=en-GB