Updated
Some AppleTV users may not see the "selection" bar that exists at the top of the header menu.
If you haven't already done so, please upgrade your app, as this was fixed in a design upgrade.
Prior solution below:
This is likely an overscan issue, and should be adjustable via your TV (not AppleTV) settings.
To check:
On your AppleTV go to Settings - Audio & Video - Video - Calibrate - Zoom & Overscan and display the image shown.
If you can't see the edges, this is due to overscan on your TV.
Adjust your TV's zoom or overscan settings to adjust the image so that you can see the "Full Screen" Area.
There is nothing to adjust on the Apple TV, you have to use your TV's settings.