Adding shell script to $PATH is still not executing properly
The best way in your case is to cd to the projects directory that you are looking at and run the shell command from there.
executables can be run from the PATH as you have tried but also it you give the path to them.
So for project1
cd /Users/My_Name/desktop/projects/project1

then run the script using a path
./scriptname.sh

or use the shell directly
sh scriptname.sh

If you are being taught the teacher should have good reasons to believe you already know this or they should have provide a book or other notes to describe how unix shells work.