Originally Posted by Eric F

Unless you have some realistic expectation of being able to compete at the pointy end of your age group, don't worry about how you might place, and don't let it get in the way of doing the event. Spend the time between now and then improving your fitness (ride a lot, and be consistent), dropping some weight, doing a few other races, and improving your bike (within the limits of your budget). On race day, do the best you can with the fitness you have, and enjoy the experience.

EDIT: There is no "embarrassment", regardless of how you finish.