How do I act like I'm no longer interested without being rude?

This girl at work, I thought I was into but I ended up getting turned off. I'm not sure what her thoughts were about me but we would always smile and wave at each other randomly despite not knowing each other and I definitely showed that I was interested. But now I'm not. What are some ways to act like I am no longer interested without coming off as if I am pissed off or being rude?
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