Hi Paint girl
way to go on the century ride. My suggestion is to either buy a rode bike or a mountain bike. Every person i know who has purchased a hybrid has been unhappy with it.
Since you like the position of the mountain bike, i would suggest buying a very light mountain bike and put slick tires on it. This will make road riding a lot easier (plus you have the added bonus of perhaps trying mountain biking in the future).
good luck and happy riding
Han