How should i get a low body fat percentage?

Great Job eating healthy and sticking to your sit up and crunch routine. Fat on the body works kinda funny. At least losing it does work funny. You can't do a bunch on crunches and sit ups and lose fat and tone your 6 pack. The reason for this is body fat is lost and burnt throughout your entire body not one area. So doing crunches isn't going to burn as much fat as jumping jacks or running simply because the energy demand is lower. You need to incorporate your entire body in exercises. do some running. Do some wall sits and push ups. Make sure to use the whole body to lose the fat.