Today was teacher-parents conference day. The teacher was going to give report cards of the students to the parents. 

I heard from my close friend,A, that during the time where A,A's parents,  and the teacher were talking, the teacher mentioned how I and another close friend of mine had worse grades than her. I was like WTH. No teacher should compare their  students. Especially that I am close with A and  I know A's parents quite well. Because of that teacher's comment , I am afraid that the parents won't trust me and asked B to stay away from me. 

Another thing was that I had another friend,B. B is in my circle of friends. That teacher just had to tell her parents and her that we are bad influences for her which made her grades went down. in that teacher's opinion , B might feel peer pressured so B lowered down her grades to be the same as us. I knew I got bad marks, but I had never stop her from studying and such. That is just low. I always did my works at school, how am I a bad influence ?  I felt falsely accused.  There was actually a possibilty of that happening,  but why should that teacher  expressed  teacher own opinion and assumption. Moreover , it has only been less that half a year that teacher taught us. 

In addition, that it weren't only me and my close friend's name were brought. A friend of mine was also brought. 

I told my sister about what happened. She told me to report this teacher to the headmaster. She said that this teacher would probably blame it on me again when my friend's grades fell, and this would convince the parents to keep their kids away from me. I would like to report this teacher to the headmaster  , however I am afraid that this teacher wiould ill-treated me and our student-teacher relationship will be bad. 

Please tell me what to do.