Why did she give me a wrong number? What did I do wrong?

Me and a girl were sitting close to each other in my school's enrollment center. We were both waiting to be seen, so I started talking to her about her classes and all. We chatted for a bit and it was going well. I made her laugh. So then I asked if we could trade numbers so I could give her tips about the school because I had been going there for a while. She said okay and gave me a number. So I waited until I had finished what I needed to do, then I texted her, said hi and asked how her sign up went. Some person replied that I got the wrong number. I don't understand why she did this or what I did wrong. It kind of upsets me because it makes me feel like, no matter what I do, it isn't good enough.
Why did she give me a wrong number? What did I do wrong?
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