I did the exact same thing my junior year of high school, I joined the forensics (speech, debate and performance) team, and my very first event was congress. I was pretty terrified too, but it actually went really well. Just tell yourself that your performance isn't a big deal, and that no matter how you do, you'll have done well just by trying it. You can also remind yourself that three minutes is a miniscule timeframe in the big scheme of things. One thing that helps me with anxiety is mindfulness. I mentally take myself to a safe and calming place, and stay there until I feel better. Good luck, I hope everything goes well!
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"Survival is insufficient" - Seven of Nine
Diagnosed with ASD level 1 on the 10th of April, 2014
Rediagnosed with ASD level 2 on the 4th of May, 2019
Thanks to Olympiadis for my fantastic avatar!