your stats are similar to mine im a bit over 9 1/2 but im taller.
sit ups are useless, firstly, if your doing to it burn calories they burn very few, they only tone. Even then they arent too effective at toning.
If you want to tone your stomach Id recommend the plank look it up. Its the best for toning abs.
Do a bit of cardio to burn calories. Even if its just skipping in your room, thats a good one, you can watch something at the same time. warm up with jumping jacks, and use them for when your taking a break from working out cus they still keep your heart rate up, whatever you do dont just sit down if youve just been excersing, walk it off just leave it for a while.