If you have the stylo module you could compare the notes from that to see if the midi→cv module is consistent. If you have a multimeter you could check its pitch CV changes by 1.000V for each octave. The most likely issue is the oscillator’s scale not being set correctly, there’s a trimmer potentiometer on the oscillator module (labelled 11 on diagram) which needs a very small, flat-bladed screwdriver to adjust it. I wrote a short article (from of a series) with an accompanying video on how to tune this.