It is a charity ride and not a race and there is no reason why you shouldn't be able to do it. Just get out there on your new bike and ride until the day comes. June is ages away LOL. Plenty of time for getting your mileage up. You also have a nice lightweight bike with great gearing which is nothing like your hybrid, that in itself should be great motivation, heck, just sign up for the 100 miler. The fun of the day really adds to the distraction of the distance, are you in a group?