I haven’t checked to see if there was a film on mine. It looks good based on your plots so I would say leave it.
Also you need to right click on the map and set home to EKF Home point and that should allow you arm it.
It’s all laid out here pretty nicely !
https://ardupilot.org/copter/docs/common-optical-flow-sensor-setup.html#common-optical-flow-sensor-setup