you can't do that, because bash creates a new shell every time you type a new command. The shell script will change directory, but it will then quit leaving you with your original shell and the origial directory.
for your idea to work, you will need to run the script as
(a dot a space and then the name of the script)
therefore delete the line reading
and run the script as
therefore, there is no need for the script to be executable.