[Build Help] Having Trouble Installing an Antec PS into a Corsair Case

I am trying to install an Antec 750w into a Corsair Carbide 400R, and when the fan on the PS is face-down (like it's supposed to be), only 2 of the 4 screw-holes in the PS line up with the holes in the case. Is it okay to use only 2 screws to secure the PS? Is there a reason that they are not lining up?

Thanks!