How do I run 1 instance of rsync / rclone script using flock as a cron job?

Question

I'm trying to run only one instance of my back up script as a cron job.
I know I can do it with a function that checks if the process is running:

if pgrep -x rclone >/dev/null
then
    # rclone is still running, backup is not done yet, exit.
    exit
else
    # rclone is not running.
    # start backup.
    /path/to/rclone/script.sh  
fi

But after some research, I found out flock should be used instead of looking for process ID, in crontab -e, in this case, run the script every 30 minutes:
*/30 * * * * /usr/bin/flock -n /var/lock/myjob.lock /path/to/rclone/script.sh

Running the command above requires sudo. Therefore, the script asks for sudo password, and never runs. (I ran the command above manually, that's how I found out).

How exactly do I use flock? Do I type a variable in my script that injects the sudo password when flock asks for it? (I know it's not secure, so there must be a different way to do this).

I tried to research this subject but couldn't find any good answers that explain how to use it properly.

Thank you.