How to properly bend a living hinge for a box?

Hello, I need to render a box project, but I am having trouble getting the spine of the box to bend properly. I’ve tried different methods, but the box either stays open or does not bend evenly.

Here is my project so far. How can I get the white extrusion (spine) to bend over the green curves evenly, like a book?

Box Project - Rhino.3dm (12.0 MB)

This is my file, and the parts are on Layer 05 and Layer 04. Thank you in advance!

Hi Julia - probably the easiest is to Flow the object from a curve like this


to a curve like this: