I race as a Cat 1. and can average about 19 mph for 50 miles too. Learning HOW to race is much more important than having the fitness to lay down a super fast TT. I've had the chance to beat riders in races that are much faster TT riders than I am, just not as good at managing energy output (sucking wheel).
Get comfortable in a group ride, in tight quarters, do lots of accelerations from 15mph to 35mph over and over again, learn how to turn, to pedal through turns (and when not to) and you'll be fine.
-SD
https://www.kickstarter.com/...bike-for-the-new-era