If all three monitors are connected to the same video card, you should be able to just choose the "Enabled and cloned with monitor #X" option in the DisplayFusion Monitor Configuration.

If they're on separate video cards, Windows won't allow you to clone them. In that case, you can try the DisplayFusion "Mirror Monitor" functions when the monitors are in extended mode instead.

On the Settings > Function tab, you can assign a key combination to the “Mirror Monitor” Function. When you press the key combo, it will prompt you to select which monitor to mirror, and then output that monitors display to a new window on your current monitor.

Hope that helps!