You need to change the zoom mode in your TV settings. Some TVs have a setting called "just scan" or "fit" or something like that. Some rare TVs don't have this option, and that's when you need to change the overscan settings in your device.

Where's that setting?

Are these setting on your TV, or on the Android software?

I have mine set to about 95 or 97% (mi box). It cut the picture at 100%. This is after trying many resolutions and ratios. Everything works out though (the one weird app is the Playstore, but that's crap) No clue why.

Sounds like your TV's aspect ratio needs to be changed.