Eek! Tengo miedo!
Tomorrow I speak with my teacher in Oaxaca on the phone. I can fool her on email - she is so proud that I am writing in Spanish - but a conversation and over the phone especially. Some of those three paragraph emails take me over an hour!
I want to please her (and understand what she is saying, since I know she will want to try to speak to me in Spanish) and I am so nervous that I won't know a thing she is saying and I will get all tongue tied. (hmmm....how could I say tongue tied in Spanish?)
I know I'm being silly! She is a lovely person and will understand if I can't do it very well. She knows I did not speak Spanish at all 3 months ago. But I have performance anxiety. I'll let you all know how it goes.
7 Answers
Your teacher knows that you are learning. I am sure she will be very forgiving. This is a great opportunity to practice speaking. Think of it as a game and not so much as an assignment. Laugh at your misstakes, learn, and have fun. I begin all of my Spanish conversations with, "Estoy aprendiendo el español". I am learning Spanish. It seems to work. The people that I strike up conversations with are impressed that I would even make an effort to speak Spanish. Then I proceed to butcher the Spanish language. 
¡Buena suerte!
Mi aviso (my advice):
Speak in short sentences.
Be so happy this is happening.
Don't try and pretend you get it and hope you will, there's no way. Blandly agreeing doesn't lead to understanding, it leads to great misunderstandings.
Don't be afraid to say "Perdon, otra vez?" or "Como?" CONSTANTLY or you will be totally at sea.
Try repeating what she says, then the meaning will jump out at you (since we usually practice our new language by listening to ourselves (je je) not real people! My best way: Yo creo que dijo.... (I think you said....) This gives you practice and allows her to elaborate. It's FUN!
RELAX and let your brain put it together.... and give yourself time. You're so lucky! Wow! Una maestra qui quiere hablar contigo! Yo quiero prestarla.
Cand said:
I always start with "Lo siento, no hablo bien español.
It's something similar for me.
I can speak Spanish really well .... when I'm not nervous! Because I know this I always start with "Lo siento pero soy un poco timida" (I'm sorry, but I'm a bit shy). After a few minutes of conversation my brain relaxes and I do fine.
You'll do great. All of your studying and learning of vocabulary will come back to you when your not so nervous.
Besides, Oaxaca is a great place with super nice people.
¡Buena suerte!
A couple of useful phrases on the phone.
Dispensa no entendí lo que acabas de decir - Excuse me I did not understand what you just said. A little longer than cómo but it shows you have been taking the language seriously.
Puedes hablar un poco más despacio - Could you speak a little slower.
Good Luck
I am feeling the same! I started to learn Spanish to be able to comunicate with people during my trip to Peru, as I was told that English is not commonly spoken there. Now, when only 2 days left to my trip, I feel that I do not know any Spanish word besides "gracias" and "si, señor". I'm very curious how my Spanish will work. Yes, that will be a real end-test for my Spanish course! 
I always start with "Lo siento, no hablo bien español. ¿Puede usted hablar mas despacio por favor?" and say "perdón" very often!!!
don't worry I'm sure it'll be a good experience
I think you can express 'to be tongue-tied' as 'quedarse mudo/a'
I would say 'ay perdón, me quedo mudo'
And always remember 'cómo' if you don't catch what she says
Good luck
