My model has larger differences because I used Magnesium and Titanium, which have larger differences in CTE than Steel and Titanium. Also my geometry is different with thicker walls.

Your model still had an 11% higher Normal Radial (X) stress in the Axisymmetric model than the Plane Stress model.

Plot the Normal Axial (Y) Stress in the Axisymmetric model and compare that with 0 from Plane Stress.

You can look at equivalent stress if you want. Normal stress lets you compare directions individually, while equivalent stress mixes them all up into one number.