You have the right to be nervous, but you are going to absolutely have the time of your life. Disney is going to do a great job helping you when you get there. Plus, there are so many people in the same position you're in. I knew alot of ICP's who never wanted to leave, and well, alot of CP's that didn't either. Americans love Australians. You're going to meet alot of great people.
Good luck!