One week prior to the championship, eat a higher carbohydrate diet (60% carbohydrate calories), average protein (15% protein calories) and lower fat (15% fat calories). Drink cold water (at least 8 cups per day) as dehydration will reduce your performance by 30%.
For instance, if you eat 2000 calories per day, then you should aim to eat about 300 grams of carbohydrates, 75 grams of protein and 33 grams of fat. The carbohydrate, protein and fat grams can be found on the new food label. Continue the higher carbohydrate diet for one week after the championship to replenish your glycogen (glucose) stores in your body. Then return to eating your regular training diet. A good training diet would include eating a balanced diet and a variety of foods.
Your target weight is 170 to 196 pounds. Considering your age and sport, I am not surprised that your weight is low. You may need to eat 5,000 calories per day just to maintain your weight.
A good reference for you would be a sports nutrition book by Nancy Clark who is a Registered Dietitian.
She looks and lives the part of an athlete. Check out a bookstore or your local library for one of her books
