How do you know you failed the interview? Did they tell you that you didn’t get the job? I’ve had many interviews that I felt I “flopped” because of my stutter but ended up getting the job. And others where I thought I spoke well and didn’t get the job. Try to focus on what you want to communicate to the interviewer and what image you want to project and don’t worry if you stutter. We are usually much more critical of our speech than others are anyway. And remember that people who don’t stutter still get turned down for jobs. Keep at it!