Good luck returning the game if it's been opened... I could send you copies of countless electronic retailers return policies, nearly all of which specifically preclude the return of OPEN, UNSEALED gaming products...

You cannot return opened electronics, it's always been that way unless you can flirt with someone and get them to exchange but doubt that will happen, only happened to me once. Gamestop let's you but it has to be within 7 days.

You might be able to trade it in but you won't get much for it. Probably won't get a refund unless there's something physicaly wrong with the contents of the box.