Chill
It'll be a guaranteed PB! Nearly everyone gets nervous before a race...it's mad, but we do. Even for races where I know I can do the distance, and have absolutely no chance of winning I get nervous.
Start at the back, don't go off too fast (very easy to get carried away!), and if you start to feel wobbly, slooooow right down but keep it at a run, not walk. Then you'll make your goal of running all the way.
You're doing fine for a "newbie in October". Celebrate your success.
Now, time for a mug of cocoa and off to bed for your big day Santa...