I don't have that option - it doesn't show.
That's a problem. This option is the default WordPress option. It should appear as soon as you enable the Jetpack Tiled Galleries. If you disable the module, the option disappears, but the number of columns reappears:
http://i.wpne.ws/PpGj
Is there a way of forcing it to more than the default 3 columns via code?
As long as you use Jetpack Tiled Galleries, that won't be possible.