FordGalaxy is right, the band brake is supposed to pull from the other direction.
The rotation of the clutch is counter clockwise. When applied the friction of the band helps it to grab and squeeze the drum tighter for a lot more stopping power. Having the band tighten the way it is installed will make the band want to loosen as it is applied the result is much less braking power.
You would have to flip the band around and move the fixed portion to the rear. You can still route the brake cable as you have it but the movable portion of the band should be on the front.
Also you need slots either in the bracket or on your engine plate so you can tighten the chain when needed.
I hope you understand what I mean...
Danford1