Cycleops Magnus calibration on CVT using MTB

just getting into biking last summer and now I bought a indoor smart trainer. bought a trek x caliber 7. The calibration process required me to pedal somewhere between 19-24 mph for 2 mins. Is it really that tough? I can feel resistance from the trainer but could only do 10 mph. Seems like I have to go all out in my highest gear for 2 mins and I don’t for see that happening. I’m pretty sure  I can do 20 mph on summer roads. I got my height and weight put in there correctly. What about my bike info? Does that make a difference? Im just using the defaults for the bike. Also, did swap out MTB tire for road just for trainer.

P.S. I am 53 yrs old and just want to stay in shape and have fun riding as well.

Thanks in advance!