What is a good exercise to lose a "gut"?

I'm already very active, I'm a rower and exercise with my team at least 2 hours a day 5 days a week, however I still have a gut. I'm a 16-year-old girl, 5'6" and 137 lbs with a lean and muscular build, and the gut is just really killing me because as it is I'm trying to shed a few pounds around my inner thighs however that's going a bit easier than this whole gut business (although additional thigh workouts would be appreciated as well). Help?