Revealing mistake: When Grace takes off, Beth drives around looking for her. It's raining out but in the shot in front of the car it's not raining.
Continuity mistake: In the fight scene with Jake and Beth, he throws her against a mirror and it shatters completely. The next morning it is complete again with just some cracks in it.
Continuity mistake: Beth's tattoo disappears then reappears in different shots.
Revealing mistake: When Beth is telling the deceased Grace a story of how "[she] can keep a promise", you can see Grace's body moving up and down, clearly indicating that she is breathing.