I'm in a major pickle, help me?!?

So I've been cutting since 2009, (5th grade)

I'm in 8th now. Someone told on me in 5th grade and my mom was so mad and she grounded me. She hated me for a month.

So tonight I was cutting(on my hips) and all of a sudden i cut my arm. It's in the middle of my elbow and wrist and I'm not sure how to hide it or an excuse for it. I was thinking of telling my school counselor, to finally get help, but I'm afraid my mom will find out. My school counselor and I are very very close. She was the music director and helped me sing, I spent lots and lots of time with her. I know she'll be understanding, but I know she'll tell my mom. My mom will hate me again.

What should I do?

Please help.