The crappy Windows Print "wizard" does not have much of any choice when it comes to printing non-standard images sizes. If something is not a wallet, 3x5, 4x6, 5x7, or 8x10, it makes it one of those. And if it is a small image, it gets all pixelated.
So here is my suggestion... Dump the wizard and go with a true print something that has a "Print Actual Size" selection.