Big Lots Inc. cut its full-year forecast amid declining sales of furniture and garden equipment. Slowing demand for the lawn and garden and furniture categories will force discounting and pressure profit margins for the rest of the year, CEO Steve Fishman said. Profit will fall to $2.80 to $2.95 a share this year, reduced from a previous projection of $3.25 to $3.40 a share. Analysts anticipated $3.30. The close-out retailer runs nearly 1,500 stores, including 20 in Massachusetts.