I’ll repeat the advice I gave another youngster a few months back:
1. Stay Loose (mentally). Bill Murray is the king of staying loose. He is attempting to be present at every moment. I advise you to watch every Bill Murray movie you can (seriously) especially the "good" ones like Lost in Translation, Broken Flowers, the Razor's Edge, Groundhog's Day etc AND REALLY PAY ATTENTION to how he moves through the world and deals with people. On race day (or every day of your life, really) you are attempting to be Bill Murray on the last day of Groundhog's Day: totally relaxed, confident, humble, compassionate, radiating with the holy spirit.
2. Stay loose (physically). Do a shake-out "function run" the morning of, or several hours before your race. Even 1 mile is enough. Slow jogging, feeling the good feelings of your limbs moving easily. End this run by declaring to yourself, "Damm, I feel GOOD"--even if you don't!
3. Stay dumb. This is especially for highly intelligent folks who tend to over-analyze and over-think. If you feel anxiety or nerves rising, take a deep breath, and in whatever dumb accent/voice you choose, say something like "Hyuk, I'm a gonna run like the wind today."
Side note: this also works wonders for virginal intelligent nervous types who struggle with performance deflation during physical intimacy. Stop thinking! Literally tell yourself, "Hur-dur, I'm a gonna love this puzzy." It works!
4. SMiLe and laugh. In the hours before the race, either listen to positive music that is good for your spirit (like Brian Wilson's SMiLE album) on your headphones. Or talk and joke with your teammates. Laugh freely. DO NOT BE SO SERIOUS. Go watch old footage of Haile Gebreselassie on the start line of his races--he is grinning from ear to ear. And that is at the very top of the world elite, before he rips the balls off his competitors. Your HS race is nothing in comparison to the Olympics. But even if it WAS the Olympics, you should be smiling from ear to ear. Seriously try it. Tell yourself on the start line, "I feel GREAT. I WANT to be here. This is going to be FUN."
5. Pray and give thanks for the ability to run. In the last few minutes before the gun goes off, take a moment to think of kids in wheelchairs and pediatric cancer wards. Get down on your knees either literally or mentally and give thanks that you can RUN. Think of those poor wheelchair kids and run like the wind, in an almost ecstatic physical manifestation of thanksgiving.
I'm not joking about any of the above. Take my advice, conquer your nerves, and enjoy your racing (and the rest of your life, if you're wise enough to extrapolate these concepts).
https://www.letsrun.com/forum/flat_read.php?thread=10474150#10474185