Inverting the Axis should do the trick and as far as I could find there isn't even a "Save" button, just "OK" so unless you've clicked the "X" in the upper right corner everything should be right. Double checking the Invert Axis might still be worth the effort.
Another thing to do is to press the Shift button while clicking Shut Down to shutdown the computer. That will force the computer to start from scratch instead of using potentially corrupted saved settings. Again, worth the effort.
