Viewing in a Full HD (1920x1080p) screen and opening the browser's element inspector, I saw the size of each column is 416px (screenshot 1) but your image size is limited to 250px (screenshot 2) most probably by the Retina option. Try deactivating Retina support (screenshot 3).
You're currently using the Classic Columns. You might want to try out the new Row and Grid layout systems. Check the tutorial videos below:
More video tutorials are available in our Youtube Channel and also don't forget to learn from our Knowledge Base.
Hope that helps.