Installing RetroPie to Raspberry Pi 3 with wireless Xbox360 controllers
Fixing RetroPie aspect ratio issue
10. When you are in this screen. Press A to go into RetroPie Configuration.
11. Select Raspi-Config by pressing A
12. When you enter to this configuration tool, you can use keyboard to navigate and setup. Select Advanced options.
13. Select Overscan.
14. Select No. After this you need to reboot RaspBerry so this comes in effect.