What should I do with my sister and boyfriend?

im 14 years old and well 2 days ago me and my brother was in an armed robbery and we got arrested. we both owned up that we were both with it even though he begged me to come with him.... i wish i never did it and now in 6 months time i might get a warning or go to cort and go to juvinial detention for 6 months all the way to 7 years .. if i got to cort and its a high chance me and my brother both are getting it i cant beleive it i went with my brother i did not want him to go alone and im sorry for what i did ... im getting expelled from my school also... if i was you i would and im a boy if i was you i would if she threatend to tell mum just say to her that il tell mum that you forced me to do it and threaten to bash the crap out of her i know how your felling right now im felling so bad =) everythings going to be alright you got to think of a way to get around her =) stay strong