I did something stupid, what to do?

ok im 14 =) yesturday I was really pissed off cause 1, me and my boyfriend were fighting 2, my little sister was punching me and saying loads of abusive things, so I decided to slash my arms I got like 11 scars down my arm it was the only way to let my anger out so then my sister saw the scars on my arm and phoned my mum up because she went you with her friends and my sister was telling her I cut myself with the knifes so my mum sed shes on her way… she was pretty angry with me tbh, so he came home, me and my boyfriend were upstairs trying to hide the scars up with red pen lol but then my mum came upstairs and forced me to wash the pen off, she was blocking the doorway so I couldn’t get passed but I pushed out of the way and made a run to the door, I got out and my mum still followd me she was chasing me down the street loads of people were watching but I dint want to go to her because I was scared of what she might do to me, so I ran like a few blocks away and sat behind a wall so nobody could see me then my mum went in because she had a little to drink, then my sister and boyfriend didnt see where I went so they were so they wre out for like an hour trying to find me, then my boyfriend saw me I were crying my eyes out,,, he bought me a jacket and my shoes, she took me to a phone box and rang my mum so I could speak to her like that, then I went in and I started packing my bags thn she came upstairs and tryied to stop me so I ran out again then I finally came back home because my mum was in bed but this morning she asked me to show her my arm and I were refusing to because I was saying I didnt do it :L now she does not want me to go to school because the teachers might see the scars and get involved init? I know it was stupid but I just dont know what to do to mak things right… please help ? xxx