I feel more anxious when my kids compete than I did when I was. lol
Remember when you competed. It was a lot of fun and not too many worries. That's how they feel.
Your worrying is for their feelings if all doesn't go well. But if you can look back at your own childhood, and remember that that's how they feel, it might calm you down. That's what I always did.
Easier said than done, I know.