Continuity mistake: Ruth walks to the ship, followed by Rose and Cal. When she is about to enter, the angle cuts and suddenly several women with dogs haven taken her place, followed by a lady who looks nothing like Ruth. Then in the following close-angle the group is meters behind from where they first were, repeating the walk towards the door. (00:22:15)
Continuity mistake: When Jack and Rose are in the lower hallway after escaping from Cal, Titanic is already at a major tilt with the bow completely underwater and the first class dining saloon getting flooded. The problem is that the water in the hallway is completely level and the water that floods is also level. With the ship tilted the way it is the water should have been collecting at the end of one of the hallways, not flat.
Continuity mistake: Just after Rose leaves Cal, we get an underwater shot panning down on Jack, showing that the window he's standing next to is fully submerged. However, interior shots after that show air around the upper edge of it. It's not trapped air: it's constantly bouncing around, in a wave-like pattern. (01:53:10)
Continuity mistake: In the "You jump, I jump" scene with Jack and Cal persuading Rose to get on a lifeboat, Rose embarks the lifeboat at the front, port(left side) side of deck top. Yet when Rose jumps back on the ship, she climbs back on in the middle, starboard(right side) of A deck where the windows change, running towards the bow to the Grand Staircase; while Jack is running towards the Stern from the Port front side of deck top. Jack enters the Grand Staircase from the port side of Deck top, and Rose enters the Grand Staircase from the port side of A Deck. (02:11:40)
Continuity mistake: When Rose leaves Jack's company to retrieve help, and goes to return with the axe, she stops at the stairway with the rising water and wedges the axe on the bars. The camera cuts to behind Rose to show her removing her outerwear, and the axe is still being held up by the bars but it's nice and straight, before and after this camera shot, the axe is propped in the bars crooked at an angle. (02:00:05)
Continuity mistake: When Jack and Rose are running through the dining room, both of them are completely dry and running up. After Cal tells Lovejoy he'll give him the diamond if he gets it back, we cut back to Jack and Rose and both of them are soaking wet, most noticeably Jack. (02:13:15)
Continuity mistake: After Cal throws Rose's cigarette away, she lowers her hand. Then there's a very brief angle on Molly Brown where Rose is lowering her hand again up to a point where it disappears offscreen. Then a millisecond later it cuts back to Rose and her hand is magically raised and still, no sign of her lowering it, and shortly after she lowers it while Cal extinguishes the cigarette and she places her index finger on the holder. Close-up on Rose and her fingers are in the previous position and she is extending her index finger again to hide the holder. So there's actually 2 mistakes in a lapse of 3 seconds. (00:32:10)