Here's my Happ Competition exploded. Square actuator, non-tapered pivot washer thingy, 5/16th inch diameter shaft, two rings on the shaft.

Here is the Happ Comp on the left next to the Happ Ultimate on the right. The Happ Ultimate is little longer and wider:

Ultimate has a 7/16th diameter shaft, a whole 1/8 wider than the comp, and it has the 3 rings on it for the e-clip.

Here's the Ultimate assembly. Note the round actuator that can be flipped for "4-way mode", the tapered pivot washer thingy, and the levers on the microswitches. The competition does not have levers on the microswitches while the ultimate does (because of the round actuator)

I think they gave you the wrong shaft. Sorry man.
But then again, the Competition stick I have is probably like 20 years old. Maybe designs have changed since then. The Ultimate in the picture is from 2002.
EDIT: Looking at yours again, the shaft does fit into the actuator, so it may be that the Competitions are actually that wide nowadays. Also I notice that the plastic part of the shaft/bat matches my competition and not the Ultimate. Are you sure you can't push that stick down through the base to expose the second e-clip ring? Force it if you have to, man!
EDIT2: I measured it wrong. Fixed measurements.