Recording multiple tracks via USB mixer in Garageband

I purchased the MXP124FX from B&H here in New York as part of a podcast recording kit. I wanted an audio interface that would allow me to record two hosts and two guests on separate tracks, using Garageband on my MacBook. I also purchased four XLR mics as part of the kit.

I’ve recorded one episode of the Podcast with one guest and myself, i.e. two tracks. Tomorrow I’m recording another episode and need to use three mics. I assumed that once I plugged my third and fourth mics into the mixer XLR jacks, my mac would show the additional inputs assignable to third and fourth channels. That didn’t happen, however.

And now I’m wondering whether B&H steered me wrong. Can I record from these four mics to four separate tracks in Garageband? Or, failing that, can I record the four mics to two or just one track?

I’ve alreadly learned that, for voice recording, I probably didn’t need four tracks. But I do need three and four people to sound good. Anyway, I thought I would come to the source in search of an answer. Any suggestions?