Win7 on virtualbox and full screen mode

I've installed win7 on virtualbox on ubuntu 12.04. However, the full screen mode isn't perfect. I have black parts on both sides of the screen. I tried changing the resolution but nothing fits. Anyway to fix this?

By the way, my ubuntu is 64-bit (intel 4000 graphic card), and the my win7 is 32-bit. I'm not sure if this is the cause of the issue.

You need to install the VirtualBox guest additions. Start Windows in your Virtualbox, and from the Virtualbox menu select "Devices -> Install guest additions"

Guest additions allow you a more seamless integration with the Linux desktop. Not only will you be able to have a better resolution and automatically adjust the resolution to the X window size, but in addition your mouse pointer will no longer be trapped by the Windows host, you will be able to share folders and more. See here.

Open main window of VM - Virtualbox.

Click File (upper left) or Ctrl+G - Preferences Display
Set Hint --> Screen Size the same as main system.

Done.
Back to main window, left side choose virtual system you want to start.