examples/models/02_stripes: Errorbars on backpropagated one-rdm seem wrong

Currently, `examples/models/02_stripes` runs but the errorbars seem too big to be consistent with the data. This could either be a mistake in the notebook or a deeper issue.

<img width="631" height="431" alt="Image" src="https://github.com/user-attachments/assets/a1ad2f79-a1dc-4d86-9c8f-c05d4b9ba694" />