^Just remember that nothing bad will come from it. If you mess up, sure it might be a bit embarrassing, but no-one will hold it against you
That's what I tell myself when I'm feeling anxious about something, which is a lot. For example, if I'm nervous about telephoning someone (probably cause I can't see them face to face or something) I just tell myself that because there is literally nothing bad that will come from ringing my piano teacher to say I'm not going to be able to go to my lesson that day.