How to ask a girl for her number (8th grade middle school)?

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I like this girl at my school and I want to know how to ask for her number.

Last year(7th grade), I was known as pretty weird to most but still pretty funny because I just wasn't to comfortable to step out of my box. This year though, I am known as really funny to most and although I'm not popular I'm pretty sure everyone likes me which I guess is good. I look a little bit more nicer and mature because unlike last year I am tall and I got my braces off (YAY) and I had some girls in the grade compliment so yeah. Anyways, now the popular girls are asking me to be in their montages if it's for a music video or something that they are making for a school project. They are also following me on instagram(They didn't last year)and when I followed her on insta-g because she got a new account, almost immediately she followed me back(I'm not putting such deep thought in2)

The girl who I like is really popular, she's actually pretty genuine and I know this because probably the most genuine person in the school who is my friend (she's a girl) said that only her and this other girl aren't fake.

If I ask for her number, should I maybe do it during a snowball (slow dance) or maybe when she's not with her friends?

I mean, I just want to try to keep it hidden that I "like" her and just do it in a friendly way. I know she thinks I'm funny because when I tell stupid jokes she'll laugh. I just don't want to embarrass myself.

Thank you so much,

-AZ

(Sorry for the long story)