Best bet is to ask the supplier for support since by the looks of this was built for the Pi.
There doesn't like like anything in that script that should cause problems but since it is, a few suggestions that might work.
The blunt approach would be to just run it as root via
sudo su then
./LCD35-show and see if that makes it happy. I'd tried this in a Raspbian Jessie Docker container as root after copying in boot and creating some of the directories that you should have if you have have the GUI and the script ran to completion. That said, it worked fine for a normal user + sudo too.
You could try running the command as
sudo -e ./LCD35-show in case its relying on some special environment variable, which i can't see...
sudo source LCD35-show or
sudo bash LCD35-show might work in case the shell isn't quite interpreting the lack of shebang directive at the top correctly.