If you've had an eating disorder in the past, and you're afraid that it might happen again, please seek help. It's also a good idea to check out the Eating disorder forum here.
ANyway, there are numerous ways to burn the fat. You are young so it shouldn't be that hard. Just wait until you get older! Try eating healthy, and getting involved with the family meal preparations. Let everyone get involved. If you're the only one trying to eat healthy, and everyone else isn't following the same regime it can be pretty tough. Limit carbonated beverages such as soda and other drinks high in sugars etc. Drink plenty of water. Exercise and keep active.
Don't completely cut out sugars, but be aware of your intake and be sure not to overdue it.
Also, don't forbid yourself from having all non- healthy foods. Moderation is key. As long as you don't overdue it, there shouldn't be a problem. You're allowed to indulge once in awhile!
Being chubby or anything bigger than anorexic size, can be really trying and hard, especially in today's society. Do it for yourself and your body. Health is important, but certainly don't allow social norms to get the best of you!
Good luck, and as I said before, it would be beneficial for you to visit the eating disorders board, especially if you've battled with that issue in the past. Maybe check out diet and nutrition also to get ideas on healthy ways to eat etc.