I have someone blackmailing me?

One day, I got this text from an unknown number. I thought it was a joke and ignored it. After a couple days, I got another text saying the person knew my secret, and would spread it around the school unless I told my friend she was ugly. She's my best friend, so of course I didn't do it. The person then got mad and sent an email, vaguely talking about my secret. I was then forced to give money to her, and I'm scared and really worried that she'll do some worse.