I would check the dimensions of your package. 100% means 100% of the screen, not your package. If your package is 800 X 600, you'll have space on both sides.
What are the display properties on your computer? Is the actual content off screen or is it just the window? Do you use dual screens? Sometimes my windows open slightly off the screen when I'm using dual monitors.
Have you tried multiple computers? Same or different behavior?