What is your training history? Years, # km's per week etc...

What would be an average training week to this point (focussing on the bike sessions but also good to know other legs training) including distance / time, speed, perceived effort per session.

Also position - were you able to ride the whole bike leg on the aerobars except on the steeper sections? How did you pace? Go out hard and blow up?

From the little information posted I'd say not enough quality km's at race pace... The more details you provide the more precise suggetions we can offer.