It’s hard for me to imagine being over 2 inches off in your measurements. If the receiver is significantly longer than you it’s probably going to be hard for it to be adequately supported. You might need a cell phone holder or something to help stabilize it.
I’m sure that you have no real drama mate, as long as you gave accurate personal measurements on purchasing, the good folks at Sybian would have allowed at least a couple of inches extra length to make allowance for climax. Mine wobbles a bit but that’s more because I am personally broader at the base of my shaft than what I am at the business end. I just adjust the stroke length and it stays on fine.