self esteem and leadership roles

I’m not really sure if this is the right place to post this so I’m sorry if it’s wrong!!

I got chosen to be a leader-in-training for a summer program recently, but I struggle with extremely low self esteem and self confidence. I truly do not believe I should have been chosen because I am shy and really not a good leader. I know I was the last choice too. 

I just need some tips on how to fake it. Like in a conflict situation: how am I supposed to diffuse something like that? I feel so unworthy of the position and I’m scared everyone knows and won’t listen to me if I tell them to do anything, or if I mess up and I get demoted. I need to conquer this fear because I’m really stressed!