Help! Im not at my teachers music cl for a concert..?

Well my music teacher wanted us all at the school for a concert but Im missing it! its 6:32 PM and were supposed to be at school! Im too late their singing already! I just know it! Im helping my gramma decorate the tree! And my throat is sore! And were gonna have dinner soon! I have some reasons but im so scared because I had a small speaking part and she gave it to someone else! Shes gonna be mad at me! i let her down..! D: What should I do?