Your shot was at f/2.8 (wide open and therefore the minimum DOF at a given distance). To give this some perspective... using the DOF calculator (see Sean's link) and assuming a shooting distance of 12 inches, then the DOF is only 0.03 inches.

To gain DOF, you need to do one of three things:
  1. Decrease your apeture
  2. Move farther away from the subject
  3. Reduce the focal length (different lens or zoom out)