Burndown chart only counting features which have been "Closed"

I've set up our agile board with four columns (states):

I'm using a custom field called "Story Points" to measure the estimation for each Feature. Once a feature is done, following the definition of Done, the scrum team member sets the feature status to Done. We only want to set a feature to Closed once the product owner has signed off on the feature during the Sprint demo at the end of the sprint.

However, I've now found that the Burndown chart doesn't reflect the story points of the features which are set to done. It only counts those whose status is set to Closed. I've changed the status Done to be resolved in the settings (so it's basically the same as Closed, but just has a different name), but the story points of features in the Done column still aren't being counted. If I set a feature which has been completed to Closed, the Story points are taken into the Burndown chart. But then we also lose the Feature off the scrum board, which isn't very useful for the PO, as he still needs to test during the demo and confirm that a feature has been completed.

Any idea how to solve this?