A couple of billion-dollar revenue days weren't enough to salvage Wal-Mart's ( WMT) Christmas wishes. The discount bellwether said Thursday morning in a recorded update for investors that it expects to post a same-store sales gain of 2% or 3% in December, down from its previous forecast of 3% to 5%. Wal-Mart said in a flurry of similar updates earlier this month that it was expecting the gain to be at the low end of the previous guidance; Thursday's was the first to drop the range to 2%-3%. In two of the four days leading up to Christmas, Bentonville, Ark.,-based Wal-Mart posted sales of more than $1 billion, the company said. But the surge was "too late and too little for us to reach our sales plan," Wal-Mart said. The shares dipped about 1% to $49.25 on the Instinet premarket session. Among other retailers, Amazon.com ( AMZN) fell 1.7% to $21.50.