To complete the wings, you adjust some details and improve the curvature of the trailing edges.
  orbit around the model to
               make sure the wings are even.
If any vertices seem
                  out of place, especially along the vertical axis, move them  
  to improve the wing’s appearance.
               
  (Select Object) to turn
               off Orbit.
            
  select the wingtip vertices,
               and  
  scale them down a bit vertically.

These adjustments are more intuitive than quantitative: Aim for a result that is visually pleasing to you.
  (Vertex) again to exit the
               Vertex sub-object level.
            Refine the curvature of the wings:
  Zoom and  
  pan the Top viewport so
               you can see all of the left-hand wing.
 Edit rollout, turn on  
  (SwiftLoop). Then in the
               Top viewport, use SwiftLoop to add two new edge loops that subdivide
               the long faces on the wing.

  (Vertex) sub-object level
               again, region-select vertices at the trailing edge of the wing,
               then  
  move them to better match
               the curvature of the wing, as shown in the blueprint image.

  (Vertex) again to exit the
               Vertex sub-object level.