Huh, that does seem quite slow for that wattage. What’s your weight?

Seems like most folks are in the 2.5-3.2 w/kg range for that 1:05:xx time

I did the Santa Cruz 40km which has a bit more climbing on almost that exact wattage (304w) and finished in 57:xx. Weight at ~75kg

Edit: as a thought, did you do it in Ride or Race mode? Race mode will disable drafting and I think it gives you a more aero profile