I have a star and I've created an inner border using the path effect offset feature, I'm trying to align centrally my border to my outer star, this is seemingly impossible. I select both and choose selected area, and also have tried biggest shape etc, then I click centre on vertical axis followed by centre on horizontal axis, it's clear to see the objects are not centred afterwards please help.

You have so many artefacts in your color filled shape you might need to clean up first, before "Alignment" will work properly:

I attached a cleaner version with annotations: