Nervous to perform.

What helps you ladies when it comes to getting nervous about performing oral sex on your S.O?

My boyfriend and I are having sex and has gone down on me but I’m really nervous to go down on him. He is the biggest I’ve ever had and that scares me. I’ve performed oral sex before but those penises were a lot smaller and not as thick as my current bfs. He isn’t asking or pressuring me but its something I want to do for him.