Are you looking for help to not go get one or are you looking for advice about it? If you are looking for help not to eat one, I would recommend trying to find something else that is lower calorie to eat and an activity to keep yourself busy. Even brushing your teeth and drinking some water can help keep you from eating.
If you are looking for advice about it, I'm not sure how many calories are in a whopper, but is there perhaps another option that you can choose from there or at home to help with the craving? I know some places like that make a smaller size (maybe kid sized) items that may help you get the taste, but not as many calories. Or perhaps you can make a similar thing at home tomorrow? We recommend moderation and because you are trying to make this a healthy lifestyle, having something that you really enjoy from time to time is okay as long as you account for it and make room for it in your meals.
Either way, you can make a good decision and still stick to your health goals.