I think to make things easy just reformat you card using sudo gparted if you are planning on using the ubuntu demo then just delete all partions leaving a raw blank sd then run the script. For anstrom try reformat with gparted and create the partions and include mount point, when you use gparted and create the two partitions manually you may need so set the flag on the fat partion to boot
Just a quick point of clarification before I try the suggestions. My system is Ubuntu and I’m trying to load the Agnstrom image, not the Ubuntu image.