At school a kid brought a e-cigarette to school and my friends pressured me to try it (that is where I should have walked away). I never actually inhaled I just put it to my mouth and said I did and then left. Later that day the principal found out and I got sent to the office and she said I could get suspended and they are going to tell my parents on Monday. I really messed up bad and I need help what should I do.
Learn from the experience. Yes, that is when you should have walked away, and it's probably safe to say you'll be a lot more confident in yourself the next time a situation like this comes up.
Explain the situation to your parents today instead of waiting for the school to act (or instead of hoping they don't act). If my child was potentially getting suspended, I would want to hear about it as soon as possible. Keep as calm as possible. Is it going to be easy? I doubt it – but it's going to be harder if somebody else breaks the news and then you have the conversation.
Be honest about it, with both yourself and your parents. That includes both the negatives (you caved to peer pressure, broke the rules, the school is angry) and the positives (you didn't inhale, you aren't interested in e-cigarettes, it wasn't yours, you won't do this again, you've learned from the experience [of course, whichever of those is really true]). If you want their support in talking to the principal to explore an alternative punishment than suspension, you should aim to convince them that you're aware of the mistake and that you won't be repeating it.
Generally, you should try to be mature and calm throughout. Getting defensive, getting angry, trying to hide what happened... none of those are going to help you and your parents get through a tough conversation.