Hi Peter,
I suspect the ripples could be because the spectrum is at an angle. (The camera response can also cause ripples but they tend to be broader than what we are seeing here.)
You can orientate the grating with the camera off the scope. Look at the sensor through the grating and rotate the grating until the images of the sensor produced by the grating all line up.
Cheers
Robin
EDIT – Peter, not John. (senior moment!)