The theory is that you can do one event ride that's as long as your average weekly mileage for the last few weeks before that event ride, as long as those training rides have about the same amount of climbing per mile as that event ride. It's also said that it's a really good idea to have done one long ride that's 3/4 as long as the event ride. You said your event ride is hilly. You should try some of those hills if you can, just to make sure you can get up them with your current gearing.