It's been said that the anticipation is worse than the actual event. Your mind naturally wants to fixate on the acting audition you have tomorrow at 2. That's normal. Your mind wants to analyze, prepare and worry, all of which cause you more anxiety than you need
Obviously, the best thing to do is not to think about it. Easier said than done. The trick is to keep yourself so busy before the audition that your mind doesn't have time to think about it. Fill up the time before with appointments, meetings with friends, errands you have to run, basically anything that will keep your mind off the acting audition.
When you do walk into that audition, you want to be relaxed, confident and prepared. As you're sitting there waiting to be called in to audition, don't go over the details in your mind. Talk to someone else about something that happened to you that day. That will keep your mind off the details. Don't think about how much the role pays, how big the part is, what this might do for your career, and so on.
Another thing to keep in mind is not to make this audition such an important thing in your life. Sure, you're prepared for the audition, but it's no more important a task in your day than going to the store to get milk. Having this kind of cavalier attitude will keep your anxiety in check. Of course, this doesn't mean you want to go into that audition room with an air of cockiness. There is a difference between being cocky and being confident. Casting directors want to see a confident and professional person walk into that room. Getting rid of that anxiety will allow you to be that confident person.
Just remember, if this one doesn't pan out, the next one will. Just go in there and do your job.as a professional.