The server was down yesterday which might explain why you were having issues playing. But as far as the full screen thing I did some research and could really come up with anything.
I'm not a mac person but Ill try to help as best I can.
Can you give us some more information about your system?
Did you buy the game from the app store, steam or is it on CD?
Here is link that may be helpful to you:http://forums.macrumors.com/showthread.php?t=1755239