I honestly have no idea how y'all make these things look so perfect... No, actually I do know how... Years of practice. 

Me too.I just nibbled the part around the edges till it looked round.
It depends on the colour of the cardboard that you used. If you used cereal boxes (or recycled cardstock that had been printed on), paint the edges either white or a very light grey. If you used white cardstock (that had not been used or printed on), you can either leave it "as-is" (white) or paint it a light grey.so my next question, How do you edge color the cardboard? should it be white? grey? or leave it be?