3 stringed Okinawan Sanshin inquiry

Recently got a new instrument from Japan, an Okinawan Sanshin. It’s kind of like a three stringed banjo.
I hooked up a piezo pickup, plugged it into my Focusrite, and got it to work with MIDI Guitar 2. They play very well together, but sometimes I get a few extra notes. Looking at the Poly Tuner, it looks like the software thinks that one of the other non-existent strings is being hit. I was wondering if there was a way to disable some of the strings, change a specific setting, or if there’s a plugin for it. I’ve upped the Noise Gate some and it does help reduce the extra notes, but it doesn’t stop them altogether. Having a blast with it so far. Hoping to do some really awesome things with this software.