If your video card is the one the specs listed in your profile. I would say to open up CCC (catalyst Control center) and check the monitor options. Then check in the scaling options menu and move the slider to fit it on the desktop then when you have it how you like click apply. I have to do this every time on my flat screen since it comes in a bit zoomed every time I would say reinstall drivers
or did a clean install. After that it just stuck and the screen looks correct now on my flat screen. For me it's in my digital flat panels but for you it might be a monitor since I use a tv for my computer setup. Not completely sure if it will fix the issue but this fixed it for me. Worth a try I would say.