Minoura MagRide-60D

I’ve just completed my first ride on Zwift using a wahoo speed and cadence sensor and my Minoura MagRide-60D turbo trainer.

When setting it up I noticed Zwift suggests putting the trainer on ‘L’ however when I start to ride using this my estimated power output is well over what I would expect at 300W for how (un)fit I am.

If I move the resistance up to ‘M’ it seems a bit closer - is there any way to check the settings are correct?