When I was kid I was not very confident in my skin. I had a huge stage fright, never spoke publicly. When I entered the collage high school I started to learning how to be in my skin. For my stage fright I decided to do something about it. I started to open myself more, jumping into every opportunity to speak publicly. It helped me a lot. Stop thinking just doing.
If I start to think, I just go back on my papers (ALWAYS have papers with you). Before the speaking publicly, I do some breathing techniques and trying to ground myself. I prepare for the task and always know my topic days in advance. I try not to have a big expectations and I believe that you can always do better.
Hopefully some of this things help you,