In case anyone else has difficulty getting the DNG for this exercise to the correct size:
I use RawTherapee which opens this at max frame (some extra pixels) @ 3900x2594.
First create a crop box @ 3888x2592 (which is full frame size).
Position the box with a 6pixel by 1pixel offset from the top left corner, and crop it.
Next scale that to 3000x2000.
If everything worked properly you should be able to overlay one of the JPGs with this and they’ll align.
HTH – Steve