Right now, if you are content with 3 and are still losing weight, don't change it. If you find yourself in a stall, then try adding the extra packet to kick yourself out of the stall. Not everyone over 200# HAS to have a 4th packet. I believe the original poster of that was experiencing slow losses and was trying to kick start her metabolism to achieve better losses.
If you are so inclined, after the end of the 3rd week, you can start to add in exercise and then you can also add a 4th packet if you wish. You by no means have to do this, I am just suggesting it.
Don't worry about the program working. If you are sticking to it 100% it will work for you. Also, don't hit the panic button until there is a reason to. Wait until you have had your 2nd WI and take it from there.
Started maintenance on 12/01/11
Time for a reboot. 10/13/15, this time with alternatives