By default, the Genesis Sample child theme by StudioPress centers the header image only when the header right widget area is inactive. Once you add a widget, it floats the image or title to the left.
This tutorial provides 2 solutions which enable you to center the header image inline with the search form added to the header right widget area like you see in the following demo video.
Shows the search widget in the header right widget of the Sample child theme display inline with the header image and then in a single column below the image displaying the same width as the image.
Add the CSS from style-1.css or style-2.css from the download folder, to the very end ( after the media queries ) of your child themes style sheet and clear caching.
Register or login to access the CSS in the download folder :