Hi sandra
Everything Don has said is spot on. I have terrible problems with nerves too and have forgotten whole sides of competition routines that i have been dancing for years. My best advice is:
1)Don't worry about small mistakes (Don already said this)
2)Do what you do do well (this is from a song). In other words, look good all the time by keeping your frame and posture, and not slumping or panicking when you make a mistake (i know this isn't easy - if only i could do it myself!!)
3) Before you're due on, dance some basic moves with your partner. Nothing fancy - basics. Concentrate on doing them well. At least you know when you're due on- where i am, competitions don't allow me to know when i'm due to dance except with a few minutes' notice (Are you guys looking at this!!!).
4)Walk out boldly (not arrogantly) as if you're in complete control of everything and SMILE all the time (except in dances where you're not supposed to)
5)"rescue remedy" is great (it may not be called that in the states)
6) NEVER blame anyone (except yourself) if things do go badly wrong. That's important for the future
7)Try to be philosophical. Ultimately, the aim is to be a good dancer. You'll get there.
good luck