After looking at your video again, (with sound turned up):
There should be another square centering ring (not motor mount) at the top of the stuffer tube sealing off rear blowby of the ejection charge gasses.
So, I don't have this model but I would expect at least three square centering rings: two for the engine mount and one at the top sealing the recovery compartment. If you were missing one, contact New Way for a replacement. Or make your own.
I love the NewWay kits, particularly for the "extras" they include that other manufacturers don't: Sandpaper, emery board, heat shrink tubing, launch lug guide, unique shroud line attachment, etc.