Did you do a diaphragm breathing or just a long deep breath/chest breath? I know some stutterers whose speech got so much better after learning to breathe from the stomach/diaphragm, maybe it could help you too. As for the anti-anxiety medication, Thiamine/B1 is a perfect supplement for you then, not only does it help us boost our speech/language development in general but also give some relaxation effect! Sometimes I felt I was way too chill after consuming it that I only consumed 250MG of it three times a week. And since you are in school, my advice would be to study as much as possible, be a nerd lol. At least for me, I felt like the more I studied, the less I would stutter. I suspected because my brain just focuses more on processing the new knowledge instead of worrying about my stuttering too much. Participating in sports/music-related activities will do the same effect I guess! Good luck!