How to stop being shy?

I start next monday as a supervisor, my boss says he sees potential in me but I'm always been shy with people, I'm 24 and can't get over it, also people say I look angry, lazy and sleepy but I work really hard a the laundry. One time, there was no one to cover 2nd shift and I stayed, I solved superiors problems with different guests even tough I never done that before, I just acted like I knew. I did this 2 times, then my boss came to me saying I'm smart, don't waste your intelligence in the laundry, I accepted but I'm nervous I'll screwed up socially, I don't want to let him down and regret his decision.