What volume will 11.0g of oxygen occupy at STP?

I work it out and I get 15.4L, but when I submit the answer it says it is wrong. I have no idea what I am doing wrong. I convert the grams to moles, which is .69 moles, and use the formula PV=nRT. So it is 1(V)=.69(.0821)(273). Can anyone tell me what I am doing wrong?