Trying to lose weight the smart way - 1800 Calorie Diet

Hi,

I've lost over 184 pounds, but I still have more to lose.
I've been doing a lot of calorie counting and I basically want to eat what I like but just eat less or eat the right portion, like for instance..., I want to eat Potato salad or Mash potato and the serving that I want to eat is 1 cup or 1 cup of rice for dinner, I've been reading the Exchange type diets and that if you're on an 1800 calorie diet and let's say for breakfast you're allowed 2 bread exchange, basically saying 1/2 a cup of c. oatmeal and 1 sl.of bread or you can have 1 cup of c.oatmeal or 2 sl. of bread..., I would like to do this but I'm afraid of gaining weight, but I'm not sure why I have this fear, because if you're consuming 1800 calories a day, and eating close to 600 calories per meal, then how are you gaining weight..., or am I a little confused?
Please Help!!
My Email address is: Janis18@Netzero.net