Credit Card Lounge

Okay I got a credit card by mistake about 2 months ago. It was a Bank of America Student Visa Credit Card. I nothing about history so when I got the card I cut it up and closed it over the phone. I never used it. My aunt told me later that it would hurt my credit and that I should have left it opened. I did not know because I know nothing about credit cards. Will my credit score go down? If so, by how much? Please be detailed. I know nothing about this stuff.