My guess would be for you to only have one screen on at the time. That is either the laptop screen or the TV screen. If you have both on at the same time you are just sending the exact same screen out to two monitors with different aspect ratios. One of them is going to suffer.

If you want the screen aspect ratio correct for just the TV, just shut off the internal monitor, and then use the video control panel to adjust what you want for the remaining screen.