The important thing is that you're moving forwards. To have an interview at all is an achievement, and you can take this experience, learn from it, and be more ready for the next one.  Don't be afraid to ask them to schedule a slighter longer interview to make sure you have time. That shows confidence, preparation, and also people *like* doing favours, it'll endear them to you more, it's a little psychological trick. Perhaps next time you can make sure you're in a more comfortable area, maybe ask to take a 5 minute break if you're getting flustered, whatever. But perhaps a sales role just isn't the job for you if you often struggle with stuttering