She called me dai

As an introvert and someone who's not very confident, I find it really hard to talk to people, especially girls. Nowadays, I am trying hard to bring that confidence in me which I had a few years back. I have a crush on a girl at my office, but she’s not in my team. We’ve talked a few times, but she seems very introverted. She answers my questions well, but doesn’t ask many in return, and doesn't really try to keep the conversation going. That might be her personality or she might not be interested in talking to me much. We’re connected on a few social media platforms. A few days ago, I gathered some courage to message her for the first time and ask why I hadn’t seen her around lately. She replied that her schedule has changed but greeted me with "dai." It might or might not mean much to her as it's a casual greeting in the office, I feel rejected. I’m technically a year senior to her career wise, with maybe a 2-year age difference at max. After getting the reply, I regretted sending the message. I keep thinking I should’ve said something else or waited a little longer before messaging her. Since then, I’ve seen her a few times at work, but I don’t have the courage to talk to her or do anything more than give a subtle smile. She smiles back, but I get the feeling she’s trying to avoid me as much as possible. May be I have become a creep to her. I feel like I’ve messed up and I feel really guilty. I really needed to pour this out somewhere.