You don't indicate your age. The younger you are, the slower you would probably want to take things, both for your sake and for the girl's.
Why not start by giving her a call, and just talking for a bit? You could tell her you enjoy talking to her, that having coffee with her was great, something along that line, see how she responds. Unless the girl is rather young and inexperienced, she would probably get an inkling of where you're leading with this, and this would be a comfortable situation for her to tell you that she's not interested in anything romantic. If she responds positively, you could then ask something like "what would you say if I asked you for dinner?" Keep it light, so she can comfortably back out into "let's just be friends" without it being awkward, but if she doesn't, it's a date.
If you don't want to ask her on a date yet (it's not about generally too early or not - There are no hard rules. It's about how you feel), you can text or call, tell her you've had fun hanging out with her, and then ask her if she'd like to join you for some activity that'd be less 1-on-1: if you're hosting a party, invite her. If you're going bowling with some friends, ask her to join. Something like that. Make sure she isn't the only girl there, not all girls present are your male friends' girlfriends, and that it isn't a sneak double-date. That way, you can hang out, without it being an official date yet. A double date is another option you could go for, but if that's what you want, be open about it.
