Another crappy day

Crappy day at work. Our group leader makes me nervous, I don't know why exactly but he hovers sometimes and of those are the only times I make mistakes-some small, some big. When he not over my shoulder, I can do stuff right. I make mistakes with things I do and have done dozens of times. This makes me anxious. Trying to change my way of thinking-it's not the end of the world if I make a mistake or don't do things perfectly everytime. In other words, only reacting as much as a situation warrants and not not automatically going into flight-or-fight mode for almost everything. This is harder than it seems.