After completing the hanjie, set the zoom to 110% and sit staring at the middle of the pattern. (Ignore the dots in the corners, these are to keep the frame the size that it is.)
Relax your eyes and allow the image to de-focus. You should see two blurry images overlapping (one is what your left eye sees, the other is what your right eye sees).
Then slowly bring the new image into focus.
If you have done it correctly, you should see six squares in total. The top-left and bottom-left are empty, the others will have a dot in the middle of each one. The 2D image appears a bit 3Dish.