How to not have anxiety when speaking.

How to not have anxiety when speaking. Hello, I am a 15 year old severe stutterer. Just having started school again I'm met with the same "sorry what was your name?" and, without fail, I freeze up and gradually spit it out awkwardly gaining a lot of unwanted attention . We also have to say "here" for the roll call but today, spontaneously i knew i wouldn't be able and i was right. I froze up and after 5 seconds i eventually said it. I think a large part of my stutter is due to severe anxiety. I can't control my breathing and start sweating bullets.This has led me to depression. Is it too late for speech therapy? is rehearsing my words effective? Any techniques on how to quickly spit out single words? Thanks