Hey man, I know how you feel, been there done that but I always try to look at the positive view of things, not to make myself just feel better but also to prevent my stutter from deteriorating any further in the future. Since you said that this was a practice interview and you weren’t really gunning for the job. Most likely because you didn’t care, your stutter increased. I know when I don’t care, my stutter flies through the roof (talking to family and friends and such). Keep your chin up. Things work out in the end as long as you’re persistent and work on your stutter. Best of luck,