Trying out for Wizard of Oz and I'm freaking out!!!?

Well you have one valid concern but you can't do anything about it. That is that Judy's performance truly was a clic and can't be copied. With that in mind you must KNOW the song and it's tempo and inflection, but do not try to be a clone. Everyone else will make that mistake. If you get the rhythm down you will be as close as anyone can get. Concentrate more on the actions of the number, the emotional expression of Judy's work. The clic nature is as much the song as it is her presentation. If you get the "Judy" style close the producers will give your rendition a better reception. They too know she was a clic that can't be perfectly matched. If your competition only concentrates on the song they'll miss the mark, you can't have one without the other. I'm willing to bet you do great because you really want to and that's a must.