You know that you are in a bad way. You need to get yourself to your school counselor, doctor, or it that isn't happening you need to go to your nearest hospital to the Emergency Room and tell them exactly what you told us. Since you are a minor, they will call your parents if they're not with you; that's OK because you will have no chance to hurt her or yourself in the ER. You need to be in a safe place and under most likely some medication that will help you to understand what's going on with you, and so you can start healing. The thoughts about harming your mother are just thoughts, and you are a good person to realise you need help to get rid of them. Good luck and let us know how you are doing.