AT&T texing problem? ?

My mom just bought me a phone yesterday called the Pantech Laser. I got a message reading this: AT&T Free Msg: you have exceeded $20 in messaging charges. Go to att.com/msg to learn how to reduce your charges. Omg I'm so scared! I JUST got this phone too! I have this one best friend who texts me A LOT. I have unlimited texting too! Is $20 a lot? Do you think my mom will be mad at me? I'm really nervous. I know I'm very irresponsible -_-. But don't they know the definition of "unlimited"?? Please, help, what should I do? I'm afriad my moms going to be furious at me and take away my phone, but I'm so excited to finally have one because all my friends have one!! So please help me!!