Your body burns fat from where it stores it. It's not like if you do sit ups it's going to burn fat specifically from the stomach.
The main thing is to just keep losing weight and some of it will come from your stomach if that's where it's stored. You could also try specifically building the muscles in your stomach. While this definitely WON'T burn fat off your stomach, if you build some muscle (which btw will be very hard to do while losing weight) it may make you happier with the way your stomach is looking.
With that being said, everybody's body is different. Some of us just naturally store fat in different places, so you may just not be able to get your stomach to exactly where you want it to be, particularly if you also want to keep more fat on other parts of your body.