I think it's great that you will take lessons soon, and that you plan on being honest with your instructor and tell her about your fear. I dont' believe in denying fear.
You know, it's just one of those things that you have to go through to get out of. All I can say is that in the beginning of riding, like you are, it IS scary. But, it will get less scary, and it will get less scary really fast. Once you ride in the arena it will get easier each time.
Let us know how your lessons go, and good luck and keep smiling!