Even at day 18, the egg should be full.
And, theres the issue. You should be running your still air at about 101.5F (even though the instructions say 99.5, disregard them) to make up for cool spots in the incubator. I'd leave it in, and see if it hatches late.
Your egg, to me, doesn't look full enough to be full term. At this point, the entire egg should be dark except the air cell (it looks like you've still got a bit of clear fluid on the bottom, pointy part of your egg) and the air cell should be drawn down on the side of the egg to prepare for...