PROVIDENCE, R.I. — "Get down or you'll die," the heavyset man brandishing a knife told the salesclerks at Metro PCS, 601 Cranston St., just before 6:30 p.m. Monday, according to police Commander Thomas A. Verdi.The clerks, Heidi Bencosme, 24, and Alba Hidalgo, 20, said the man was about 6 feet tall and wearing a midnight blue hoodie, light blue jeans, black shoes and a black ski mask.