Really I'm just trying to use the Ctrl+2 shortcut to make a radical, but for some reason this won't work. What could possibly be going wrong? The exponent shortcut works (i.e. Ctrl+6).
Converting my comment to an answer. On my OSX machine Ctrl+2 worked, so I checked the documentation which states under Details and Options
In my keyboard layout the 2 is the same key which is used for the @. Maybe on your machine this differs. Can you try to use Ctrl+@?