Hi, normally money blowing machines will be round, approx. 9 or more feet in diameter or 3' X 3' square, like a phone booth? The one you have already built is 3'x4'. This is bigger than I would have suggested. But the main problem is it's not square? This creates problems with the blower motor air distribution. It is also a large area to try and move a lot of air upwards with a 1/2 horse power motor, I would have suggested using a full horsepower and a squirrel cage blower. You never did tell me what the RPM's were on the motor and what type blower you have. Is it a squirrel cage blower?
One thing you can try and installing an adjustable vent in the top of the unit. One reason it's not working is the air being generated can't go up, through and out the top of the unit. With the 3'x4' floor on your unit, I would put at least a 2.0'x1.5' adjustable vent in the top of the unit. Play with the adjustments, opening and closing to try and get the effect you want.
You also need the air blowing up through the grate on the bottom of the unit over the entire area, except for 6-8 inches around the edges of the walls of the unit. You may have to build a fan shroud to accomplish this. You also need to install a ledge on the walls at a 45 degree angle to funnel the money back on top of the grate where the air is rising so the money is cycled again.
Since you already have the unit built, I would try the above to see if I could get the unit to work.
Keep in mind, the air rising from the floor of these units is really moving. I have seen advertisements for these machines say that the air being generated is moving at 150 MPH? I think that 1/2 this speed would give you the effect you are looking for.
So, try the following to see if you can get your unit to work.
1-install the vent in top.
2-Build the fan shroud to direct the air up from the bottom of the booth.
3-Make sure you have sufficient quantity of air and also air speed being generated from the blower motor.