apple tv mirroring face time from i phone - how can i get it full screen on my television?

You can't use FaceTime on an Apple TV. The only way is by Airplay Mirroring.

1. Connect to the same Wi-Fi network on your iOS device and the device that you want to AirPlay to.
2. On your iOS device, swipe up from the bottom of your screen to open Control Center.
3. In Control Center, swipe horizontally to find the Now Playing screen.
4. Select your AirPlay device

How to AirPlay content from your iPhone, iPad, or iPod touch - Apple Support