Dear Scared,
When you first get your period, the flow is usually very light, so even a tissue would probably be enough until you can get a pad. Talk to your mom about your concerns. Tell her what you know—that some girls get their periods at your age or even earlier. Let her know that you'd feel more comfortable if you could carry a mini-pad with you. Based on how you're growing, your doctor will probably have some idea when you're going to get your period, but not exactly when. Your questions are very normal, and you might want to get more information from your school nurse or your doctor.