Are you using the bridge pickup of your guitar? That helps.
Artifacts are notes you are not playing or octave jumps?
Some guitars (I got one) because of the setup tend to play harmonics when not needed. A dumper might help in that case. A slight adjustment in your playing technique might be needed at some point. It’s a trial and error process. Moreover the signal input in MG3 that comes from your audio device should not be too high (it picks up any scratches or movement of both hands) and not too low (not enough attack and sustain to trigger the Guitar to MIDI). Again trial and error. You can use the gate knob to lower probability of false notes or strike filter before the MIDI Instrument.