6WK Beginner FTP Builder

I am having an issue with Day 2 of the builder.  It wants me to put out 445 watts for ten seconds and when it comes to that interval I’m on the highest gear and blasting my pedals.  It get a reading on the screen of 350 the it just drops right down to 220 when I am at full sprint.  I have a tacx blue twist set to resistance level 3 like recommended. As well I have a garmin speedometer on my hub and a garmin cadence counter on my pedal as well as a garmin heart rate monitor.  All of which pair just nicely so I don’t think they are the problem.  Any help would be appreciated thanks.