I never uses rclone, but did you know that we can add online account on Gnome setting (Google account) and it will also give us access to Google drive directly from Nautilus (default Gnome file explorer)?
So without looking at if the script and *.service are correct and work I think what you want to know is how to actually activate the service.
should check for changes in /etc/systemd/system
systemctl enable rclone.service
should activate your rclone service and mount it whenever your system boots to multi-user.target (which looks correct, seeing that you are mounting a resource that requires network-drivers to be active)
It should also tell you that it created a symlink to somewhere (I can never remember where)
Link to my source - in case you need more info about the usage of systemd: