I do not have all the details of your interview but how do you mean bad? Were you nervous? If it was the case it is like exams in school or university. Interviewing is a skill like anything else. Try to do as many as you can to gain more confidence. Good luck in your future endeavors ;D
Quick tip, be aware of your body language and train it a bit. Doing a warm-up interview with a friend is also a great exercise, it will really help to control your voice and feel comfortable with it on the real interview.