Congratulations!
Sometimes it's easier when we don't "rehearse" for a moment coming up in our lives.
I never raced but I did run, back in the 80's. I found that, when I really got into the zone and my brain quit complaining I really didn't have any thoughts at all. I just ran. It was almost a meditative state for me. Same with walking my dog very early Sunday mornings. We were there, in the moment, walking.
You might find that you're totally exhilarated when you cross the finish line so go with it! Jump up and down, cheer, pat yourself on the back.
Dagmar