How can i control my nerves when singing?

i have to sing infront of the cl which feels impossible! im extremely shy to start with, and i have trouble even talking infront of people never mind singing! im not going to lie im terrfified about it... i know it sounds stupid but im really dreading it especially since i didn't really want to do it to start with, does anyone know how i can control my nerves because usualy my voice just goes shakey and my leg starts twitching :S please help me!!!!!!!!!!!!!!!!!!!!!!!!! thankyou in advance :)