Stress Linearization Help (1/4 Model Pressure Vessell)

Hello,

I am currently attempting stress linearization on a model of a cylinder with internal pressure applied.

The model is axis symmetric and only a 1/4 of the model is modeled and the symmetric fixture is used within Simulation.

My section plot cuts the model in half again (effectively to an 1/8 of the full cylinder). My question is how on earth do I ensure that my SCL is perpendicular to the inner and outer shell wall?

When I select the two points they are never straight, I have tried adding split lines and reference points and all have not been successful so far.

SolidworksSimulation