What can I do about this situation?

I spoke to my girlfriend about drinking, yes I have done it, only TWICE. Only because I was curious, and after that I have not touched a drop of alcohol. I told her I did not want her drinking, we spoke about it and she was fine with it. Right now I found out she took a shot of alcohol. When she told me this, my heart dropped, right now I am shaking. I have no idea why, but the problem is, she knows how I feel about drinking, I promised her I would not drink again and I spoke to her about not drinking and I’m sure she told me she would not do it. She thinks drinking and smoking is disgusting, so why even do it?! Yeah it’s only one shot, so should I be calm? Am I exaggerating? I have no idea what to do at this point. I am just upset that she did this, she is 19 years old by the way. I understand it’s fine for her to be curious, but why if you think it’s disgusting and because you told me you would not be drinking anytime soon. Should my trust in her, decrease, I am not sure how to put this, should my trust, which she has, be somewhat affected? How should I react? and am I exaggerating?