To do that, you can just disable the Prev/Next Navigation option:
The size of the slider depends on the width and height of the image that you put in the slides. The slider will automatically fill the entire width of its container and the height of the image will adjust accordingly as well. You may try using 1:1 dimension images or enable the no container option to add more space to the slider.
Would you mind clarifying what preview pane you are referring to? Is it the white space around the slider? If so, enabling the No Container option should work.
Hope this helps.