You cannot have 12.05 moles of gas at STP.
At Standard Temperature and Pressure, 1 Mole of any gas takes up a volume of 22.4 L. This is 0.0446 Mol/L.
If you compressed the gas to 270 Bar, you would get 12.05 Mol/L.
(but this hardly STP).
BTW: molar density is given in Mol per volume, not in g per volume.