Hi Ryan,
I am Naama from Editor X product team.
To ensure that you’re using the New Hamburger menu, could you please delete it and then re-add and validate if the problem is solved?
In addition, please see that while editing the menu (before Preview or Publish), you click on Open Menu to see the X. The default is that it opens up in full screen as you described.
We’re waiting for your reply,
Na’ama