I have a Macbok Pro 13" and I'm using virtualbox to run ubuntu 12.04. My problem is I can't resize ubuntu for occupy the 13" of my screen when I use full-screen mode. Ubuntu only allows me to use two screen size options, 1024x768 or 800x600. The 800x600 option is too small, and cuts the screen in a smaller size with black edges.With the 1024x768 option, i only have black edges on the left and on the right. Is there any option for extending the image at the whole screen?