Macbook mirroring does not fit TV screen

I have a macbook pro 2011 with Mountain Lion installed. When mirroring to my TV via apple TV 3rd generation, it shows only the left portion of my notebook, and this portion is shown on the right side of the TV. The apple TV's menu fits properly, and also my ipad and iphone. I´ve tried all the resolutions on my TV and also changing all the settings on System Preferences-Displays.

Any help?

Thanks,

Pablo