SMS confession was rejected. She said,' I have a boyfriend, don't send messages in the future, I won't come back'. We are colleagues. How can I catch up with her?

At least for now, she either has no feelings for you or has a boyfriend. What you can do is:

First, observe whether there is any inquiry, and if there is, divert your attention.

Second, if not, don't be too demanding. After all, you are colleagues, don't tear your face. You can show your excellent quality and ability from work and getting along with colleagues, and maybe there will be a turn for the better. So if you tell her, at least she will pay more attention to you.