Chicago rapper Chief Keef was sentenced Thursday to 60 days in juvenile detention after tearfully apologizing for violating his probation on a gun conviction. “I am a very good-hearted person,” the 17-year-old musician told Judge Carl Anthony Walker. “I am sorry for anything that I have done wrong. . . . Give me a chance.” But Walker said the teenager has repeatedly disregarded the court’s orders — including the rapper’s June 26 visit to an indoor gun range in New York in a promotional video for his music.