Very wrong, in fact. It is impossible to know if someone has been penetrated or not by looking at their hymen.

"The hymen does not 'break' the first time you have sex," Rose Olson, lead author of a review paper on "virginity testing" published in the journal Reproductive Health and a medical student at the University of Minnesota, tells BuzzFeed. "Looking at the hymen can't prove someone has had vaginal sex, or anything else about their sexual history. Everybody's hymen looks different. Even the most experienced doctors cannot distinguish a 'virgin' hymen from a 'non-virgin' hymen."