You cannot spot reduce fat. So to get rid of the excess around your stomach, you'll have to keep doing what you have been doing. Situps do not do a single thing to help get rid of stomach fat.
Simply it's calories in vs calories out. To make it more difficult you can look at the type and ammount of calories you are taking in compared to the type you are burning. Also you can incorporate timing with your cardio and diet.
I'd say keep doing what you are doing. Watch what you eat and keep doing the cardio and it will come off. This is coming from experiece. I went from 230lbs freshmen year to 165lbs at my low point.
If you have any more questions just ask.