I think I wired this the right way but I can't find an online reference that I trust enough to flip the breaker back on.
This is how I wired it.
Is this correct?
That is correct.
See NEMA 14-50R
G - Ground
If you look at the terminal screws on one of these receptacles, you may notice they are different colors.
The green tinted screw is ground.
This is a common pattern in most electrical devices, and can easily be remembered with a simple poem.
As @HillBilly.Developer pointed out, since the red and black wires are both hot it doesn't matter which one is connected to X or Y. Each hot wire will have an electric potential of 120V to neutral/ground, and 240V potential to each other. This is because in US residential wiring, the house is fed from a transformer with a center tapped secondary. So the building is supplied using two hot legs (L1,L2) which are 180° "out of phase", and the center tap (N).
Because of this, any device in the house can be powered using either 120V, 240V or both. To supply 240V to a device, a hot wire from each leg of the system must be present at the outlet.
In our situation one leg of the system is the black wire (L1), and the other is the red wire (L2). So either way you hook them up, you'll always have 120V potential L1 to N and L2 to N and 240V potential L1 to L2.