Raea,
Congrats on the job you landed. I think perhaps you are having anticipatory anxiety even thow your thrilled to be doing the job you are worrying about the "what ifs". Kick those thoughts to the curb .
To lower your anxiety and still enjoy your happiness talking usually helps. Share your feelings with friends, family, on here are all good ways to work through the anxiety.
Relaxation techniques: Try deep breathing, muscle relaxation, visualization (imagining peaceful scenes), and/or listening to soothing music.
Realistic self-talk: While we can't always control what happens to us, we can always control what we say to ourselves. It's important to keep things in perspective. Talk to yourself in reasonable ways. Ask yourself "how likely is my fear?" Remind yourself that you have coped before during other challenging times. Don't just dwell on the negative but consciously look for things you can appreciate every day.
Make an effort to stay focused on what's happening now. What do you see, hear, and smell? How do you feel? Truly be 'present' in the moment! That will help you keep the anxiety down.
And on Sunday kick butt, you will be OK. I promise if you just stay in the moment.
Break a leg...................... 
...or is that only for broadway?
Kitt