When Big Momma goes downtown with Sherry, the car is parked with the top down as Lester comes up to them. When Sherry heads across the street and Big Momma walks away to head to the self-defense class, the car is seen in the background with the top up.
Near the end, when Malcolm discovers the money in the trunk, Sherry walks in and he slams the trunk, throwing a pile of toys on top of the money. In the very next shot when he opens the trunk to show her the money there are no toys inside.
Malcolm, as Big Momma, gets hit in the face, ripping the mask. However, in the following close shot, although Malcolm was clearly slugged on the left side of his face, the rip in the mask is over his right cheek.
In addition to the placement of the necklace, the simple fact that Malcolm was wearing the necklace in front of Sherry is a huge error. The necklace belonged to Big Momma. Sherry should have noticed this.