Collimation is good. The pattern you're getting is because you took a picture of a star cluster so don't worry about the donut shape. You have a slight tilt as the donut is darker on the right compared to the left. Also a fairly big value for the field curvature but that could be because of the DSO you've imaged. Try again on another starfield more uniform (around A Crux for instance). Other than the tilt I wouldn't change anything else in the set-up. You're good to go and the pic looks great.
