Short answer: you don't.
Long answer:
As a beginning seducer there are lots of pitfalls, you moved too fast and made her feel a slut, you didn't set correct frames, your post-sex game wasn't on point, you didn't take care of her emotions, or she only wanted a casual quick lay and you misread the signs, whatever... I think I had fucked about 4 or 5 girls through cold approach before I found one who was willing to communicate with me at all after, and right now it's about 50/50, I think that's just the way the cookie crumbles... if you have really crazy value (like an incredibly toned body and you give her GREAT SEX and have super awesome game in text and in person that keeps her excited and horny and chasing) then this will improve, but for the ordinary guy with seduction skills, it's possible to get her quite excited, excited enough for sex, only for her to crash later and think "why on Earth did I fuck that guy". No matter, that's completely normal, what matters is she wanted your cock at the time, rewriting the script later is her prerogative and affects you not a jot.
But now assuming you gave her great (or good enough) sex and you sent the post-sex text and didn't lose your frame (waited a bit before setting up a meetup instead of being super thirsty)... and she's interested enough to meet up again... then you need to repeat the process 3 or 4 times until she's definitely "your girl" and you will feel the dynamic changing a little bit. She will likely ask something like "what are we" and you brush this off by saying something like "hey I'm enjoying your company right now but I'm not looking for a girlfriend if that's what you meant"... if she leaves because of this, well shit happens, you were not providing her enough value... don't lose your frame over it, be chilled and go back to cold approaching. But after some months she will get more insistent and want you to commit to a relationship.
Depending on how well you kept your frame and how much value you provide, she may put up with an uncertain situation for only a month or up to 6 months, but eventually you cave in and agree to relationship. It's good to do this on your terms, if you feel she's beginning to create drama over your relationship status and you want to keep her around, then you should consider making an honest woman of her. It's not easy being a girl with everyone looking on and judging you, and if she has a boyfriend she would like to be able to brag to her friends and family about you, etc. Especially as her close friends (who know she's seeing someone with significant lover value) will be pressuring her to dump you or make you commit. It's just how things go. What you should NOT DO is pressure her to commit. That's very weak.
Ray