I've had two SG's. The first result was good but I wanted a bit more advancement. The final result turned out very well. I used to have insecurities about my chin position but now it's my best feature.
In hindsight, it might have been better to do double jaw surgery rather than two attempts at camouflage, because I'd have the benefit of a bigger airway and possibly an even better result. Can't complain about the SG's at all though, the final result turned out better than I expected beforehand, and I don't have any lip numbness.
I doubt you'd look worse if you get a second SG, I've never seen a case where a "class 2" patient's chin was advanced too much. You'll have to consider the other risks of the surgery though.