Having SpringArm length changes translate to the scene.

I’m making an on rails game using a spline component. I want to simulate switching between different rails by having a SpringArm component follow the spline, which is the parent of a camera. I was gonna put a collision box on the camera so it can trigger crashing into obstacles. Y’know. Basic stuff.

In the viewport of the player blueprint i’m able to make the camera change positions by editing the target arm length value, but this doesn’t appear to translate to the scene, even though the blueprint below seems to return the right values and respond the button inputs. Is there a make this work?

Here’s an image of the blueprint changing the length of the springarm and the effect of editing the value in the viewport: https://i.imgur.com/VoXITjl.png

The reason I’m doing this is to add an offset to the player as they turn corners and stuff. I tried simply adding an edit to the x trasnform but obviously making a u-turn while on the left would have the player end up on the right. I’m no maths genius so some pointers would be appreciated, I am a beginner after all.