The exercise you're doing is definitely going to tone up the muscle underneath, but it's not necessarily going to get rid of any extra fat (you can't choose where you want to lose fat from, your body doesn't work that way lol) But if it's core fat you're looking to shred you should start taking CLA and eat lots of healthy fats like avocado and almonds!
The workout Tiffany said is good, not sure what its called either lol here are two you can try
*Oblique Thrusters (while in a push up position bring one knee out towards your elbow, alternate legs).
*Knees to elbows (standing with your hands behind your head bring one knee out towards your elbow, alternating legs).
There almost the same things, just working at different angles!
I think you have to workout your obliques. So you can try my WO: Carsten's Obliques Toning Pt.1 and Pt. 2. And like the others said, burn fat.
I like doing oblique v-ups and also dumbbell side bends to target the obliques directly.