[Philomath]

I really think you should try talking to the school counselor about this.
She shouldn't have to tell your parents because you are over thirteen and in the US, that is the age for confidentiality. However, if she feels that you are a serious danger to yourself and that you could possibly go to far, she will probably contact them.
I understand when you say you feel nothing. That's how I feel at times, I don't even know sometimes why I am cutting, I just do it at times for no real reason. I know that sounds weird but it is true.
You have to figure out though how to deal with why you are cutting yourself, knowing why is a good first step, now getting help from a counselor or therapist will be the next step to figure out how to learn how to cope with how you feel, or in this case, do not feel anything.
Also, I really hope you get help for this and stop soon while you aren't to far into the cycle of cutting because it can be very hard to quit and it only gets worse as time goes on. Stopping is easier to do when you are not to far into it but that doesn't mean it's really really easy, it just means that finding alternatives and using them is easier to do sense your mind will not be as focused on it as it is with someone that has been cutting for a very long time.
I really hope this helps and if you ever need help or just want to chat, you can PM me.