Hello, Why do you feel so down all the time? What is making you feel like this? It's best that you find out the root of the problem and then use that to find a solution so you don't feel like that anymore. Have you tried talking to a parent, trusted adult or school counsellor? If you haven't, then I suggest you tell someone what is going on exactly.
I don't know why your friends are not taking the cutting seriously. In fact, cutting is an extremely serious issue that is becoming more and more common amongst teenagers. Why do you feel that you have to result to cutting in order to feel better? Trust me, whenever you have problems, talking about them with people that you trust can make a huge difference. A guidance counsellor will be more than happy to hear you speak and then offer advice on how to solve the problem. Self-harm will not solve your problems - they will make matters a lot worse.
Here are some helpful links that you can read up on:
Cutting Information
Guide to Self-Harm
153 Things to Do Instead of Self-Harm
Help with Self-Harm
Self-Harm Information
I understand that you are in a really tough place right now and you feel that nothing is going right in your life. That is an extremely common feeling that comes with depression. I am not one-hundred percent sure that you are depressed, but it looks like it from this eHelp. I suggest you get help immediately. No one should feel the way you do and I am truly sorry that you do feel this way. Please try and seek help.
I hope I've helped.
If you ever need anything, feel free to message me anytime. My inbox is always open.
Good Luck,
~ Sabrina