Yeah - you could certainly tweak it - I only actually did the above mockup initially to try to illustrate how to think about it for the person asking the question at the time
If I were to tweak it, I would leave the "Create Custom Challenge"and "Quick Match" field titles, because it is helpful to have words describing the overall action that those fields cover. I would change the text to be "Custom Challenge" and the button to be "Create".
I think that the tidiness of the 4 buttons in the "Quick Match" square with the time setttings for quick matches outweighs the small difference that happens when you press the Computer button.
Sure, conceptually you could say that the Computer button is more of a "Custom Challenge" in that you get to select all the settings for the Computer, but overalll it belongs up there because in all cases you expect the game to be started by OGS, not by someone clicking "Accept".
That said, the other way of arranging it would be three buttons in a row for "Quick Match" and two buttons in a row, below them, for "Custom Challenge", defining the Computer button as a "Custom Challenge". This would also work intuitively.
The main thing to fix is having some easy to grasp functional grouping matching the visual grouping.
I didn't refine the mockup because to do that you need to be able to match the button text font, which would be some messing around to achieve