How to take a full nude??

I’m talking to a boy and he wants a full nude. I’ve only ever taken booty or tit pics, not my whole ass naked body. He’s asked me a few times and when I say no he’s super nice about it. I’m 18 so don’t the nude police don’t need to be worrying. How do I take a flattering one??? I’m fat so that’s what I’m worried about lmao