Images not showing up full size.

Hi. I created a new site using the Bosco theme a couple of weeks ago. When including images in my posts, I always select center-align and “full size” for the image, which has produced nice images that span the maximum width of my site. Recently, however, the images started showing up smaller (more like the “large” size, I think), even though I’ve continued to select “full size” when posting the images. Initially, the images were as wide as the post title, now they’re only as wide as the post text (which is narrower than the post title). Any help would be appreciated.