After the Captain and the shark expert and the policeman are all out looking for the shark, they are supposed to be way out in the ocean. Well, throughout the movie, you can see just how close to shore they are. The camera pans, and you can see the shore just a few hundred yards away.
In reply to Quint Hooper and Brody being out in the ocean and then the shore appears listen back to when Quint blows the engine on the boat he tells the crew that they are heading back in to shore so that would explain why the shore appears even though its still a few miles away.