This is a "feature" of your laptop. Usually when people experience this problem, I can find some obscure keyboard shortcut in their laptop manual that fixes it, but I'm having a bit more trouble with the VAIO.
The best instructions I can find are these:
After booting the laptop, right-click the mouse to bring up the graphics properties dialog box. Under the heading “Graphics Options,” go to “Panel Fit,” where you will find settings for screen size. Make sure “Full screen” is checked. If it is checked, try the other settings to see if this solves the problem.
If you still have trouble, let me know the exact model of your laptop and I'll see what I can track down. Either that, or contact Sony and tell them "I get black borders when I play games with a smaller resolution than my laptop's native resolution."