Hi
The game always launches from the expansion that was the latest release from EA, regardless of the order you actually bought and installed them. In your case, University Life is a more recent release than Generations, so the game will launch from Uni Life. The game therefore sounds as though it is doing the right thing as far as that goes.
Instead of opening the game via Origin, instead go into Applications on your Mac hard drive, look for the folder called The Sims 3 and launch by using the base game icon in that folder. When the game launcher opens, look at the small icons along the bottom and see if Generations is coloured-in or still greyed-out. If it is coloured-in then the game is probably installed. You can start playing and make sure that Generations content is now included in your game. If it is still greyed-out then the game has failed to install properly and we'll have to try again to install it.
Caspin
