Can somebody help me, I'm freaking out!?

You're 13!? Why do you have an iPhone to begin with!!!? Your mother doesn't want you in a chat room becuase they are dangerous, and you can get yourself into trouble. You need to own up to what you did and explain to your mother your mistake. It is better to be honest with her than to have her find out that you tried to hide it. Life is about making mistakes and learning from them. Best of luck!