Spacer is missing.
The spacer with the hat (5) goes on the sprocket side, the spacer that's actually a collar (4) goes on the brake side. As I recall, it's about 1 inch thick.
Poke them into the dust seals of the wheel before fitting the wheel back in the swingarm and have your brake bracket sitting in the inner groove of the swing arm. That will space your disc at the appropriate position.
I use a ziptie to hold the bracket to the swingarm while I slide the rear wheel in place.