The best way to see if things are working correctly is to gently turn the engine over in a clockwise direction looking at the shutter face, as the piston goes down you should hear the noise from the valve opening, if your shutter is too lose then the air will come out that way rather than through the valve, it should take very little effort to turn the engine this way.
If you now turn it anticlockwise there should be a lot of resistance as the piston rises as the valve and shutter should be closed.
If that snot clear let me know and I'll take a short video.
A slight bend in the shutter rod will push it further against the face but go gently as you don't want more friction than needed.
Engine is looking good so far.
J