When in a retroarch game hold your designated hockey and press F1 on your keyboard. This will bring up a GUI. You can the select which aspect ratio you would like. 1:1 PAR will be the original systems intended ratio.
1:1 PAR has never worked as intended on my widescreen LED TV, I always get the screen stretched out fully to the sides on both 4:3 and PAR 1:1. No idea why. I’ve tried editing the boot/config.txt file with the force aspect ratio and auto ratio lines too but it’s always the same for me. I ended up editing the aspect ratio manually instead with the retroarch GUI using the custom mode and squeezing it to what I think is 4:3, saving it for all emulators. GPsp is still stretched out though, I haven’t found the config file yet for that one.