Are my parents right, or am I?

i would say neither. you are 18 and are old enough to make YOUR OWN choice. But on the other hand, she is right when it comes to not going because it is a once in a life time opportuinity(sorry, spelled it wrong) and she doesnt want you to miss out on it. Besides, life shouldnt be bed on your looks and how people remember you for. Just go for the sake of it and then laugh it off with a couple friends. Its just a picture, not the end of the world.