There are numerous continuity errors when the chef is cooking on the stove top, including disappearing/reappearing oil bottles and the cart that the chef first brings over missing in some shots.
There are two things wrong with how the ducky tie bet went. One: both parties agreed on calling the initial conditions off - so Lily would not be able to decide on her own to just go back to them. Two: the bet terms were that Barney can do everything the cook can, and not that he would be absolutely flawless in his performance. A second try would have proven that he can do the trick.