Three Columns Image Alignment Issues?

Three Columns Image Alignment Issues?

I'm trying to create an email campaign which features three columns of images with a button underneath. Despite advertising the three column layout with the ratio of 33:33:33:, for some reason the layout automatically changes to 34:33:33 which screws up the alignment of the button underneath.

I've tried everything such as changing image size, but it all seems to be down to the fact that you can't change the ratio of sizes. Can I do anything to fix this?