At least you have 2-3 weeks yet! Like the others said, just keep practicing, have a backup plan but don't aim for the backup plan, and focus on your music rather than the audience. Can you play with your eyes closed? Maybe if you wouldn't have to see the audience, you could better imagine they aren't there. Or, practice in front of a family member or a small group of friends a couple times first. Just believe in yourself and don't overthink it! Sometimes, the worst part of doing something is just the anticipation, not the actual act itself.
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