I just bought Portal 2 and already having a problem?!?

I just bought the PS3 version of Portal 2 and it comes with a free PC copy. I already had a steam account and played many games with it but when i linked my PS3 to my steam account and tried to enter my CD key for the PC it says its already duplicated and there for invalid?!. However my steam account still gets the achievements I get from the PS3 and i can see my steam account on my PS3 and all my friends just no Portal 2 in the games list... I bought it bran new sealed in plastic today. I tried restarting steam multiple times and entering the code. Anyone else have this problem?