Pegging my boyfriend

So… my boyfriend is really into pegging and I want to do it for him, but I don’t have the muscle and I’m too scared. He’s asked me why I’m scared and I can’t tell him.

We’ve done it once, where he rode the strapon. It was great and I loved the power, but I’m too scared to make the next move to actually being the one go for it. I couldn’t sleep last night because he made a post on fetlife (we’re both on it and we’re openish so not cheating) where he made a post about wanting a girl to peg him.

He obviously wants more and I want to give but my own anxiety about not making it good for him is holding me back?

Anyone into pegging who can give me tips?