When I was installing it, it said installation failed and it does not show up in my launcher or applications. However in the my games section of Origin it says it is installed and only gives me an option to play it and not reinstall. The "play" option takes me to my launcher where it is not installed. Origin won't let me uninstall it, and I cannot from my Mac because it was never completely installed in the first place!
Follow instructions here: http://bluebellflora.wordpress.com/the-sims-3-on-a-mac/how-to-do-a-clean-uninstall-and-reinstall-on-... to see if everything is gone from your mac.
It's best to search for any left over folder if that doesn't help. Especially search for any folders called _Installer
I don't work or have any association with EA. I give advice to the best of my knowledge and cannot be held responsible for any damage done to your computer/game.
Please only contact me via PM when asked to do so.