I have antivirus but i got a virus?

Hi! I just got a new laptop and best buy recommended i should get Trend Mirco Titanium for my Sony Vaio E series. So i did, cuz i really dont know much about laptops.. Anyways, Now something keeps popping up saying that my windows 7 home security 2012 needs to be updated or something. Im so confused. Its says I have 32 viruses... IM SO CONFUSED! what should I do? I dont have a credit card, so I cant buy it online... Help????!!!