Girl help??????????????

i'll try and make this brief but i cant promise anything lol So, i work in a bank as a teller (yes im a guy and there are guy tellers). there's this girl i work with who has started to become flirty over the last couple of weeks and we talk a bit but not as much as i'd like too since we usually only see each other at work. I recently got bbm and she was excited that i had a instantly added me and everything was good. For the last week, she's been saying how she doesn't have a bf and don't know if she ever will because she's had a few bad relationships in the past. So last week i decided i'd ask her out for coffee and see what happens from there. The only thing is, i didn't do it in person but over bbm! I know that was stupid after the fact and im definatley going to fix this but i dont know what to do. Should i wait for her to bring up the bbm msg or should i just tell her what happened and ask her out in person???? *** FYI, she didn't say no to the bbm msg. she said she was sorry and had plans and we should do it another time. So, what do i do? Apologize about the msg and just ask her out then and there or wait for her to bring it up and just go from there?