Do you have a link with the slider active so I can see whats going on?
This is a copy/paste from one of my comments here – http://appfinite.com/topic/genesis-responsive-slider-off-center/#post-6574
“the Genesis Responsive Slider images don’t center, they float left or right, but they don’t center. This isn’t caused by the theme or anything, that’s just the way the plugin itself is designed. You can change the width to 1140px to fill in the entire space which will make it appear as centered.”
You should also download and run a plugin called Regenerate Thumbnails anytime you change or add your image sizes. This will adjust everything instantly for you so you don’t have to wait for the images to resize.
I create awesome sites for awesome people! Contact me if interested – ericsanchez1585@gmail.com