Take two extra bites every time you eat, once you feel full. It will stretch your tummy a little, and make it easier for you to eat a larger protion. Don’t overdo it, because later in life you will probably regret it. You could eat higher caloric foods, but I don’t necessarily recommend that, because it will likely be unhealthy. Although things like legumes (nuts, beans like pinto and black beans and chickpeas) are healthy, have fiber, and also are highish in calories.