NeckerVD - that's what I also found out. Three changes minimum, not two changes maximum.

My plan was to go to Chur then onwards, which requires one change, which I understood to be two changes.

I told you where to change in my post 20 above.
You may change at Chur instead of Landquart. You will then have to leave Pontresina 1/2 hr earlier.
https://www.sbb.ch/en