Hi
It might be because of the resolution of the shape extrusion is not high enough. In the Shape Extrusion module, try increase the the Resolution parameter in the Path tab. If the issue persists, and to rule out any resolution related cause, increase also the Resolution parameter in the Cross tab, and the Cache Density in the Spline's inspector.
If the issue is not resolution related, please send me a reproduction case.
Have a nice day
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Maybe the Rails game object is not centered? You can define an offset of that game object in the Input GameObjects module, or in the Tab "0:Group" of your Input Spots module. Let me know if this didn't help.
Have a nice day
Please consider leaving a review for Curvy. This will help a lot keeping Curvy relevant in the eyes of the Asset Store algorithm.