How do I [20M] ask a friend [19F] to be fwbs, knowing we are very close and our relationship has been very platonic?

I (M,20) have a friend of mine, she (F,19) is really close to me, we have been friends for over 5 years and our relationship is very platonic,today, we were talking about our past and we went into deep detail about what we did with other sexual partners and what were our turn ons and what we liked specifically, i mean, deep deep detail, and i was thinking, why would she share all that with me if she aint attracted to me, and i started having thoughts about us hooking up and stuff, what should i do?