Step 1:
Prefold in half, then fold both edges to the centerline.

Step 6:
Fold the upper part in half two times, then backwards over the light pink line.

Step 5:
Fold both corners to the spots indicated by the arrows.

Step 2:
Fold both edges to the centerline and unfold the model.

Step 4:
Fold the corners just a little off the center.

Step 3:
Repeat steps 1 and 2 in this direction.

Step 10:
Fold the edge in half, do the same on the other side, see pink arrow.
Then press the model flat again.

Step 8:
Fold over this line and turn the model.

Step 9:
Fold both corners inwards.

Step 7:
Fold over these two lines

Step 12:
Curve all three parts and glue them together, see next picture for help.

Step 11:
Fold the lower part straight upwards.

Step 13:
This is how the backside of the model looks.