I get really bad anxiety in large crowds, working with customers, and in school. Which makes it hard to focus and remember?

I was reminiscing this math test from when I was way young. I did terrible on the test cause when the teacher was talking I was focused on the other kids. I remember thinking oh that kid hates me or she thinks I'm weird.just a bunch of irrational thoughts. I get overwhelmed with my own thoughts, I couldn't even focus on what's the teacher was saying. I have the same problem now at age 25. I worry so much with irrational thoughts I can't even focus. My question is are there techniques on reducing anxiety,so I can focus