Oh! your PICO-8.sh should only have the first line (I accidentally had a typo, sorry about that )
SDL_VIDEODRIVER=x11 DISPLAY=:0 python /home/cpi/pico-8/pico-8-volume.py
(assuming you downloaded the py script to that location)
I am sorry again for that typo.
If you look at the script, line 107 https://gist.github.com/follower46/69cdc41d9dc09cf9fe97b48ec4036158#file-pico-8-volume-py-L107
It launches PICO-8 for you.