Leave the left hand crank arm off and just concentrate on your Sprocket arm.
Add the thin washers to move the Sprocket out and remove washers to move the sprocket in.
Its about as simple as that.
Use something straight to check the alignment or look from behind the rear wheel along the freewheel to the sprocket to see if its aligned.
If it looks about right the it should tighten up correctly.
The sprocket can't get any closer to the BB when its tightened due to the spacers/washers!
You could even try this without the spindle to calculate the correct number of washers but its far easier with the spindle in!
Just give it a go!
So long as you have a removal tool then it wont take long to remove the crank and add/remove washers if you cock it up!!