A Boston-to-Provincetown ferry that ran aground Saturday was back in service Sunday, according to Coast Guard Petty Officer William Trapnell. He said the vessel, operated by Bay State Cruise Co., underwent minor repairs, passed Coast Guard inspection, and resumed service again at about 9 a.m. Sunday. On Saturday morning, a skipper-in-training steered the ferry, the Provincetown III, onto a sandbar in Boston Harbor. No injuries were reported, company officials said. All 149 passengers were transferred onto another Bay State ferry. The trainee steering the ship was fired.