After Boi and Countess run off, Roger and Sharpay are seen scouring the theater looking for them. They finally end up going out a fire exit into the alley. During different shots of the ensuing dialog, the fire exit door behind them appears as open then closed.
In an actual Broadway production Amber Lee would've had an understudy, meaning that when she quit her understudy would've taken over, not Sharpay.
(at around 47 mins) One of the characters says, "she'll discover the real meaning of going home in a doggy-bag". The actual expression refers to "going home in a body-bag", not a doggy-bag.