How can I play game without internet? (boxed version)

I bought the retail version of the game so that I could play it without the internet and steam, however when I installed it, it installed it without the disc. Does this mean that as soon as I lose my wifi connection like when I get the train back to uni later I won't be able to play it? If so, how can I alter settings so that I don't need the internet to continue my game.

Help would be appreciated

You only need the internet to activate the game. If it's activated you can set steam to offline mode and play the game wherever you are.