Please read step C again. It does not matter where your drive is currently mounted at (e.g. /media/pi/PiStuffs). You create new directories and mount your drive /dev/sda2 in step D at the new location.
I am 99 % sure you did not (you did edit something in /etc/default/plexmediaserver.prev, correct?). You have to do something like this:
Btw: Please also read the official PMS on RPi guide.
