It's the cable for sure, I had the same problem. Need to line it up properly in the depression.

 

cable fits perfectly and still the airbag sits inside, all day playing with the steering wheel nothing, also plug everything and the horn is not working

 

I've had dealers (I don't like fooling with airbags) change steering wheels/airbags on 3 different 997's and never had a problem - I think you should find a different dealer or maybe try an independent like RAC near the Addison Airport.

 

maybe the springs need to be stretched out or replaced or maybe the back of the air bag plastic body is collapsed , but otherwise it is the wrong air bag