What should I do if I get an erection while sleeping with my best friend?

We're planning to hang out on my birthday, and go to her house after, and sleep together. I'm a 16 year old guy, she's a 15 year old girl. Now, I'm afraid I'll probably get an erection, since I'll be holding her in my arms, our legs will probably be touching, maybe even our genitals, and I'm pretty young too, so you know, it's not that hard..plus I find her really attractive, which makes it even more possible. And we might be in our underwear sooo.....(don't find all this weird, we've always been really close, I mean closer than siblings..like in a relationship, but without the kissing and the sex..)..do you think she'll feel weird, or uncomfortable if she feels my erection?(which she probably will, since we'll be so close..). If I notice she felt it but didn't say anything, should I say anything, like crack a joke about it to make her feel more comfortable or something? Thank you very much:)