It's a self-fulfilling prophecy, essentially. At least it was/is for me, and it seems to be for you. You think that anxiety causes stuttering, which leads to stuttering in anxious situations, which leads to more anxiety, which leads to more stuttering, etc. The only way to stop this, which I've been attempting myself, is just working on self-confidence. Not much else I can say, other than I've made large improvements and believe that you can as well. What helps me the most is realizing that people don't really care; at the end of the day, people think about themselves and not about you. You being mildly disfluent will not be thought about by someone else 6 hours later, so you shouldn't care as well. Good luck. You got this.