When Junilda “Muñeca’’ Diaz went to the Berklee City Music scholarship concert Tuesday night, she thought she was there to play bass and support her friends. Little did she know, she was about to receive a four-year, full-tuition scholarship to Berklee College of Music. After her performance, the 18-year-old Charlestown resident listened as Lee Whitmore, the school’s vice president of education outreach, and social entrepreneurship, called the names of the scholarship recipients, and was surprised to hear an extra one awarded. “I never thought once it would be me at all,’’ she said. “I had no idea.’’ She screamed and ran up to the stage. “It was just like ‘The Price Is Right’,’’ she said. Diaz was one of eight students to receive a full scholarship at the event, emceed by actor-comedian Sinbad.