Family Help, please answer!?

I was talking with my mum about violence in media, and I asked her if they would sell teen and mature rated video games to young children, she didnt know. I told her my older step sister went and saw the kings speech and didn't get stopped to my knowledge the movie was rated R. My step dad didn't really care and my mum was really upset because he always justified my step sisters decisions and doings. They fought for at least 10 maybe 15 mins when my sister finally came out of the shower and she said he didnt know it was R, turns out in Canada its only PG-13, she's almost 16. My mum told me never to talk about her doings again, and I think she's quite upset with me. My step dad is totally normal maybe even happier. I told my mum I was sorry but she said nothing. What should I do?