In the movie, the necklace was tossed into the ocean. In real life, it’s going to be kept under lock and key. British jewelers are creating a sapphire and diamond necklace modeled on the fake one worn by actress Kate Winslet in the film “Titanic.” The real version, being made by Asprey jewelers, is expected to be valued at $3 million. Asprey is using a 170-carat Sri Lankan sapphire and 107 diamonds weighing a total of 36 carats for the necklace. It will be sold at auction March 21 in Beverly Hills, Calif. All proceeds from the sale will go to the Diana, Princess of Wales Memorial Fund and an AIDS charity.