From the Help....
To turn the Magnifier window on or off
Click the Magnify button.
If you unintentionally opened the Magnifier window and are unsure
how to turn it off
The Buttons tab displays a list of the commands to which each button
is assigned. Locate the button assigned to Magnify, and then click
that button on your mouse.
I suspect it may be easier to reassign the button and use the
Magnifier as below:
To open Magnifier, click Start, point to All Programs, point to
Accessories, point to Accessibility, and then click Magnifier.
To open Magnifier using the keyboard, press CTRL+ESC, press R, type
magnify, and then press ENTER
At least that way you can Exit the Magnifier
....Alan >> Stay informed about: How do I turn off the screen magnifier?