Im scared, im being sued for copyright? what do i do?

hello well firstly im a student and i seriously got no money at all. i purchased a study guide from a teacher to study for a test to get into graduate school and i had to sign a document saying i am the purchaser and ill not make illegal copies etc so i did. i bought it but now i decided i do not want to be in this field anymore so i just sold my copy and i seen ppl selling their copy of this study guide on the web too. i tried selling it on ebay but i didnt do it right cause apparently i posted it twice again after i already sold mine and sent the package to the person. the teacher who sold me the study guide saw the 2 posts on ebay and bought both and sent me an email saying hes contacted his lawyer and they will be using my signed form as proof and they will do litigation against me. im so scared i just sold my copy and i didnt make multiple its just mine and i dont know wha tto do i just messaged him saying i did it on accident but theres no response, idk what to do. will i be in big trouble? help.