The red shut off should be either at a perpendicular position (off) to the flow or in line (on)with the flow. Even though you can put this valve at a 45 degree angle, this is not a position.
When you turn on your bottle, have your pressure adjustment screw backed out counterclockwise all of the way. This basically turns off the regulator. If you still here the hissing, be certain that your regulator seal between the tank and regulator is not damaged.
If you still here hissing, the internal components may be loose or defective. If you are mechanically inclined, you could take the bonnet assembly off and check the seat assembly and diaphragm.
Link to the
regulator and select the replacement parts tab for a exploded view and list of regulator parts.