Duckular, do you have any pics of the incubator? Does it have a fan? How about a water pan in the bottom? What size light bulb are you using?
An incubator without a fan will need to be set at a slightly different temp than one with a fan.
What kind of incubator? Still air or forced air? Brand/type?
And . . . you said chicken incubator, but you have a duck avatar. Which are you incubating?