I know what the specs are but just wondering if I could get away with using it in a 3 x3
Generally speaking, the more light you give cannabis, the greater your crop yield and crop quality. To maximize your growth, you should get your plants to their light saturation point, which, for cannabis, is 800-1000µmols. If you look at
the PPFD map from AC Infinity, you will see that the Ionboard is does not generate enough light to reach that level even at the very center of the light even at the lowest hang height*. As soon as you move off center, light values from the fixture roll off very quickly.
I'm not knocking AC Infinity; in fact I'm a big fan of AC Infinity. Their products tend to be well thought out and well-engineered but their are the exception. My advice would be to return the light and get a
ViparSpectra XS-1500 Pro. It's the same price as the Ionboard but delivers
significantly more light than the Ionboard and, due to the increased red in the spectrum, will tend to grow larger plants than the Ionboard. Check the PPFD maps at the link to see the difference.
If you do use the Ionboard in a 3' x 3' space, you should expect a modest harvest. That light, even in a 2' x 2' space, isn't creating a lot of light so your plants will not be able to make much food. When you go from 2' x 2', which is 4 square feet, to 3' x 3', you are doubling your area and the corners and edges of the 3' will be getting barely enough light for seedlings, much less the 800-1000µmols that they should be given.
One idea for the 3' - Mars and Spider make bar lights in the 3' space. You could get away with 2 XS-1500's for a bit less but I don't skimp when it comes to parachutes, radar detectors, or grow lights.
*The high readings from small areas in the center are not material.