Jetpack Tiled Gallery Width in Thesis 2

Hey guys

I’ve just tried out the Jetpack tiled gallery in one of my posts, and it will not fill the content column width, it defaults to 500px instead of the 760px I desire.

I read about this on another closed thread which said to add the following code to custom.php, which I have done, but there is no change. I also tried re-saving the gallery and post after adding the new code but still no change.

Anybody got any ideas?

The code:

if ( ! isset( $content_width ) )
    $content_width = 760;

Thanks for reading ??