Can you post your spec people will be able to help more knowing what components you have and also how does it not fit the screen is it too large or not filling the screen ?
If you havn't already go to control panel and adjust screen resolution then select the advanced option and another window will pop up click the troubleshoot tab and run that.
Do you have a control panel for your integrated graphics if so you need to try to change the scaling setttings in there, if not try an uninstall/reinstall the drivers for the monitor and graphics.
The simplest solution would be to connect using an alternate cable.
If you have DVI I would go right ahead and use that (the quality is exactly the same) though if your only other option is VGA it's worth getting this sorted.
Problems with overscan when connecting a PC via HDMI are very common. Normally you can correct this via the graphics card control panel. In the case of integrated graphics chips I'm really not sure how to go about doing this.