Hey whats up man, hopefully you didn't go just yet before reading my reply. If you already did, how did it go?
Anyhow, here's what I recommend you try...
This may sound a bit funny but it really does work..
1. Make sure that you give yourself enough time. (rushing to get ready to not be late will only elevate your stress levels and trust me, that’s not a good way to begin.
2. Eat a really good and super healthy meal which will be easy on your stomach yet give you a satisfied feeling and energy to have fun. (DO NOT let her know you ate beforehand!) lol
3. Take a warm 30 minute bath which will calm your nerves and ease any physical or mental tension and don’t even think about the date.( Even when you’re on your way to her house or on it, remember that she is more than likely WAY MORE nervous than you!)
4. Look your best and pick you a fashion-appropriate outfit that you can be comfortable in. (When you are happy with looking your best, your self-esteem will soar and your confidence will naturally put you in a relaxed state of mind.
5. If you do at any point temporarily start to think about the date, immediately distract your mind with something funny as laughter is the best cure for anxiety. (YouTube college pranks, or Bizkit The Sleepwalking Dog and laugh your ass off as a distraction)

Stick with these instructions and you will be more than fine.