Apparently Simon thought he was playing with a guy called Andy, yet when Finn's first message to him appears on Simon's screen, Finn's name is clearly visible.
Just before the thieves head downstairs to the basement, the napkin is sitting up like a mountain near the cookies. When the thieves escape the house as the Baxters return, the napkin is folded.
At the end of the movie when Finn and Mason are throwing snow at each other, it's evident that the ground is covered in a white sheet and not snow.