Yeah thats due to the slider. I haven’t seen an easy way to make the genesis slider images center since they can only float left or right. Most of the time it only appears to be centered when adding the slider to a widget area with a width defined but it’s actually floating to the left or right…..you can look at the demo for an example.
If you only plan to use 1 image, just add the image in directly and add the css to make it center and it will work that way.