Your service is starting, as is evident from the logged message "Started My Shell Script."
It's odd that you're using sudo in the script. The script is already run as root by the service. Also, sudo asks for a password, but you can't give it one because you're not running it from the terminal. Xrandr doesn't even need root
I believe the error message is happening because xrandr needs the DISPLAY environment variable, which is inherited by applications launched from the desktop (e.g. by the "startup applications" feature of your desktop environment, from .xinitrc, or when running it from a terminal window)
See https://wiki.archlinux.org/title/Xrandr#Configuration_using_arandr for something you could try