The person in this thread: https://www.petrockblock.com/forums/topic/force-43-screen/ said setting video_aspect_ratio = 1.175 gave good results. Or you can change it in the emulator (if it’s a Retroarch core) by accessing the GUI, think it’s f1 if you’re using a keyboard or you can map it to your gamepad/joystick in retroarch.cfg with:

input_enable_hotkey_btn = "**" 
input_menu_toggle_btn = "**"

(the stars are where you specify the buttons on your controller)