Summarize the following:
You have a plan in place in case this happens, you just need to go through the steps. Remind yourself that you are not the first person to start their period this way and you won't be the last. It may help to mentally repeat, "Calm down. Relax." Your teacher is there to help you. Wait until there is a pause in class and approach their desk. You might say, "This is my first period. What should I do?" They will then give you some options, such as visiting the nurse or the restroom. Ask your teacher for a pass to visit the nurse or go in between class periods. Let her know that this is your first period and she will provide you with supplies and advice. If you are achy or hurting, let the nurse know that as well. Say, for example, "My stomach has been cramping for the past hour or so." Your parent can bring supplies up to you, such as pads, and can go over what you've already planned to do in this situation. They can also remind you that it will be okay and that what you are experiencing is perfectly normal. Find a private place, like an empty classroom, to talk with a trusted peer. Solicit her advice on what your next steps should be and how you will feel moving forward. You might say, "I've started my first period today and I'm not sure if I can participate in gym class. What do you do?"

Summary:
Stay calm. Tell your teacher you're having your first period. Talk to the school nurse if you're not comfortable talking to your teacher. Call a parent from the front office if you don't feel that you can talk to an adult at school. Ask a friend who has already experienced her period what to do.