Most Americans surveyed in a recent poll think that even if there are problems with her marriage to Prince Charles, England's Princess Di should "stick it out." The Jan. 27-29 issue of USA Weekend magazine says that 60 percent of those asked think the princess, who is scheduled to visit New York City next week, should stay with the prince. Another 26 percent think she should opt out, and the other 14 percent feel "it's none of our business."