Former Beach boys leader Brian Wilson says he was a little nervous "but real confident" when he went on stage in a surprise miniconcert with the band at the Spectrum in Philadelphia Tuesday. It was his first public gig in years. Wilson did it again Wednesday, joining the Beach Boys for a three-song mini-set at the Centrum in Worcester, Mass., where they split the billing with Chicago. Wilson had a falling out with the Beach Boys but said the relationship is improving. He plans to join the band again at the Nassau Coliseum in New York.