This gallery has a fixed width of 550px so takes up 550px from the left hand side of the browser window. If the browser window is wider than 550px , then you will see empty space to the right of the gallery.
If you want the gallery to dynamically resize to fill the width of the browser window (no matter what its width), then set the gallery's width to be 100%.
This gallery's dimensions are too small to display your main images any larger.
SimpleViewer reserves enough space within the gallery for the specified number of thumbnails and the remainder is used for the main image.
If you want your main images to be larger, you could reduce the number of thumbnail rows from 2 to 1 or increase the size of your gallery (by increasing the height of the gallery, using a large fixed pixel value, or by increasing the width of the gallery's parent container, the content column on your page).
You could also prevent SimpleViewer from scaling down images (which may be required to respect the aspect ratio of the images) by setting imageScaleMode="FILL" which will ensure that the image area is always completely filled (though this may result in large images being cropped).
SimpleViewer Support Team