AT 100 is harley
AT-200 is single channel "universal fit" (you cut the sensor cable to length) setup.
And yes, AT-300 is what you should have ordered.
That said, I would call or email dynojet and ask them if the module itself is identical across each kit and if only the number of gauges and modules varies. In that case, maybe you only need to buy another wideband o2 sensor and any necessary cables. the wideband sensors are bosch sensors that can be bought from dynojet, or elsewhere (do a search; I think there was a topic on here about that). This may be easier than the alternative- but either way will work.
Good luck and post up if you need any advice or feedback along the way.
2011 Victory Kingpin 8-Ball
Tach / Dual front discs with Vesrah JL pads / Penske shock / S&S Intake / PCV & autotune / RPW Thor exhaust with homemade custom baffle / Tsukayu leather "Strong" bags / Avon Cobra *Radials* / Ness Vegas Peg Conversion / Ness Vegas driver's seat / Custom T-Apes from BR Custom Cycles