You don't say how much flab. In fact you don't say much of anything. You can not lose flab just by eating salads. You have to exersize as well. There is a fine line in the balance of the nutrients you need. At your age, you should not be worring about a little flab. My advice is to seek guidance from a coach at your school, or from your parents. With either choice, they can guide you using research tools that you may not be aware of.
Salads are only the beginning. Weight loss in any program is 80% or more from what you eat. Start eating clean and more often ( i suggest a 6 meals a day plan). For you that might be much but it consists of snacks between every major meal. Keep in mind that with the added snacks your portion size should be controlled.