I have just used a Megawhite teeth whitening gel tray at home, and I am not happy with the results. My top teeth appear to now be two tone very white on the top half of my teeth but darker on the bottom which is unsightly and upsetting, Is this a common problem, and is there anything that can be done to correct this, or improve my now two tone teeth? Any advice you can give would be greatly appreciated. Thank you.