Character mistake: When Katie's husband arrives in town and confronts her on the night of July 4th, he says "I miss you Katie." He does not know her name to be Katie as that is the name she created when she came to town. He is married to Erin.
Revealing mistake: In the scene where Josh Duhamel and Julianne Hough are in the row boat, it starts to rain so they rush to shore. They huddle under a tree and you can see behind them that the rain is only falling right around them - only slightly further away on the lake there are no rain drops hitting the water.