The only way to ride fast in races is to ride faster in training. Riding hours of 18-20 mph in training, will only make you really good at riding 18-20 mph. Ride hard and even, ride your downhills hard and your uphills "easy".
I did about 40 minutes of 20 minute max power(mp) (about 10k time trial pace) last week. I was riding my intervals about 12 watts higher today. This week I hope to get another 40-50 minutes of 20mp riding in. I actually expected this 12 watt improvement and think I can get another 10-12 watts by next week. Follow up that week with 8-10 watts improvement and I'll be ready to race!