Attach 21I to 21C by following the curve (make two sets).
*You will find a short blue line in the center of the side that needs to be attached. Follow that line to attach, starting from the center to the outer side.
Attach 21A to 21C and 21B to 21D (make two sets each).
*By aligning the green lines as shown in the diagram, start attaching from the center to the outer side.
Attach 21A and 21B to 17B and connect each. When doing so, make sure that the glue tabs of 21E-21H do not get misaligned.