How do i know my guinea pig is pregnant?

ok,i have a female guinea pig named Zoey and my friend has a male called Patrick. my friend brought her male guinea pig over for a play date. we put the two of them in a cage together and set up a video camera so we could see them from the living room and patrick mounted zoey and he keeps doing it to her and when i try to take one of them out they bite me. so it has been going on for hours now and i cant seperate them. ok we got them apart but can she get pregnant just from that? and if so how can i tell she is pregnant? and our parents are going to kill us if they find out and zoey is pregnant! how can i hide this from them?