i accidentally went to obscene site?

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i am in a big trouble. I was surfing for some University admission form information and after finishing with that i felt bored so i went to some jokes site(clicked on google link). It silently opened a popup in background showing obscene, inappropriate text and pictures. I immediately closed it before it could load any images when i realized it was being loaded. It was some sort of ad or popup. I went away without any thing like deleting history. It was my mom's phone with default android browser(Gingerbread)
It's been weeks now (i didn't even remember it) My useless workless evil sister show it to my mother and enjoying it. Now mom will tell dad. What should i do? I swear i didn't do any sin. please help. I don't even remember it exactly.I am 17 year old student.
For people saying it is not a big deal... it is a huge deal.I am seriously studying for getting into college and that devil(sister) is 21 year old and yet not in college. She tailord the whole story.. i watched her do it.. then i remembered it.This will disturb my studies if parents harass me for a thing that i DID NOT DO