It’s a Raspberry Pi 2 running the most recent Retro Pie version and it’s composite output

Oh man, have you got an actual CRT?

Anyways yeah, to add to what Floob has said, I believe you need to alter the various overscan values in /boot/config.txt

overscan_left	number of pixels to skip on left

overscan_right	number of pixels to skip on right

overscan_top	number of pixels to skip on top

overscan_bottom	number of pixels to skip on bottom

Tweak the values until the video output fits comfortably inside your display.