LifeLine TT-02 Fluid Trainer + Garmin Speed Sensor 2 + Mountainbike gives super low watts and speed?

Hi all,

So I have a LifeLine TT-02 Fluid Trainer + Garmin Speed Sensor & Cadence 2 + Mountainbike with a Schwalbe Insider tire - 35 - 622 (28 x 1.35 - 700 x 35C), but when I’m using Zwift this setup gives me only 22 watts (20kph and 61 RPM) avg when I’m peddling pretty intense. I’m using the 27x1.25 tire on Zwift, since there is no 700 x 35C tire to choose. I also set the tire size on my Garmin Connect app to 2174mm. But that doesn’t work. Anyone has any idea how to fix this?

Thanks!