Being blackmailed by cousin?

okay so i am 16 my name is jake and my cousin elizabeth is 12. we live close so we see eachother very often and she usually just walks in. so one day i was home alone and nobody would be back for hours. so this is embarrassing but i decided to jack off cause i hadnt in a while and christ im 16. this is even more embarrassing but i had a pair of panties in my hand while doing it, it makes it easier. anyways i dont wanna be graphic about it but there i am in my room in the middle of it, sitting at my computer desk. all of the sudden the door swings open - it was closed but i didnt lock it, knowing nobody would be home for a while. elizabeth is standing in the doorway staring at me in shock. i froze - what the heck am i supposed to do. she looked at me with my hand down there and covered her mouth in shock. after a few seconds of shock i grabbed a towel and covered myself up. elizabeth ran to the bathroom and eventually came back. she asked me what i was doing and i told her nothing i was just changing clothes and i should have locked the door. she knew what i was doing and said she was going to tell my parents and everyone she knew. i begged her not to and said i would do anything if she wouldn't. when i said anything, i could tell her eyes lit up with ideas. she is always one to try to humiliate me and mess with me on any day. so she told me she had an idea - she was also home alone for hours which is why she came over, her parents told her to. instead, i was going to go to her house with her for a while. it didnt seem bad at all until after we got there. i figured id have to deal with her being annoying for a few hours. then she came downstairs holding one of her dresses in hand and told me to put it on. i laughed and asked her why she would think id ever do that. she told me i agreed to do anything and that if i didnt, shed tell everyone what she saw and make it sound even worse. i continued to refuse for almost 20 minutes while she convinced me to by saying if i just wore the dress for a little while itd all be over, finally i knew she wouldnt let up and i said ok, if you leave me alone afterwards. it was a long pink dress and i went into another room to put it on. when i came out she laughed her head off at me, calling me a little sissy girl and saying how cute i looked. so embarrassing. then she pulled out a camera and started taking pictures. i ran away trying to avoid it. i tried to get the camera so i could delete them, but she hid it somewhere i didnt see. she said now she had pictures of me in her pink dress and could show anyone so i had to do what she wanted. after pleading for a while i realized she could make me do anything now and gave in. i said id do anything just dont show those pictures please. she seemed to love this and was calling me her little girl now and said id have to wear her dresses all day. she made me wear underwear and bra as well and gave me a makeover. i wanted to cry it was so gross. she took pictures every new outfit i wore and posed in them with me. she then took me to her room and made me lay in her bed in the most feminie embarrassing short pink dress. she said i was now under her power forever and that whenever we were both home alone i would come over and play dress up or else. i had no way to get the pictures and if my family saw id never be able to live it down. so i agreed because i had no choice. she laughed and said i was such a cute girl and made me walk home in her dress, which she said i had to keep hidden in my room. i walked down the streets trying not to be seen but it was so scary being in a dress out in the open. people pointed and i began to run til i got home. i finally got it all off and hid it away. since then she has made me dress up 3 more times. i need out, she makes it worse and worse every time. what can i do? if i do anything bad she will show everyone the pictures and i would never be able to leave my house. HELP