@andywar65 You said you're new to crontab. Quick tip: add these two lines to the top of your crontab and then any error output from the cron job will be emailed to you which may yield a clue as to what is going wrong.
# This executes a script using my virtualenv python installation.
*/15 * * * * /home/my_username/my_virtenvs_dir/my_virt_env/bin/python3 /home/my_username/my_virtenvs_dir/my_virt_env/lib/my_scripts/script.py
Also included, a line in my crontab that executes a python script every 15 minutes within one of my virtual environments, just the directory names changed.