The abused becoming the abuser

Hello! I never believed in the abused becoming the abuser, but here I am. My mom is a very hateful person, coming from a hateful background. I am underage, so I can't cut her off nor her toxic behaviour. I noticed just yesterday that I am mimicing her act, poking fun at my friend when she had a migrene. I feel so darn awful for that, but I am glad that after apologizing to her she didn't just forgave me. She told me not to apologize to her, because I can't change. I don't know what to do and how to deal with that problem. I have became the monster I was afraid of. I became an exact copy of my mother, who is also mocking me, screaming at me and physically hurting me. I am so lost. I don't know what to do with it. How can I go back? How can I stop being an awful person? I want to be a soft and kind person, but yet I hurt everyone, that I meet.