If you're new to using gsync make sure it's actually running. You can enable the on screen display for testing in the Nvidia control panel, and if your monitor has a built-in refresh rate counter like mine does you can also use that to verify. The refresh rate should fluctuate from the max/default or at least go to whatever you have it capped at (you should cap a few FPS under) depending on your frame rate.
Gsync can be really finicky at times, depending on the game. I've had it setup correctly before (or so I thought), only to have it not work or crash/hang. I go reset all the settings to the same values or reinstall my video drivers and somehow that fixes it. Point is, it's touchy.
Also, as others said above you want vsync ON in the nvidia control panel but OFF inside the game's settings. You should also use RTSS or a game's built in FPS limiter to limit your framerate to a few frames below your monitor's limit. For example, if your monitor is 120Hz then set your limit at 117 fps.