Muscle does weigh greater than fat, with your exercise I doubt you'll have much fat. You can do your own BMI or go on the NHS website where they take you through some easy steps and give you a calculation of your result. However if you want a better result seek your GP.
There is also the skin fold test, it's like giant tweezers, that don't hurt. They measure the amount of fat in different places on your body. This is done without grabbing the muscle. This test will also give you a body fat result.
Personally I don't think you need any of this, what your worried about ismuscle and there is nothing to worry about, you are just toning.RRemember you are only young and going through changes in your body.
Probably not.
If you can do those Track & Field events that you have indicated, then your definitely not overweight.
The way to test fat is to have someone test your BMI. But not everyone looks the same, and if you do as much exercise as you say you're probably the envy of others you don't even know about.
No. You are not fat. Muscle is heavier. You have great energy. When your 13 year old body becomes a toned 16 or 26 year old body, there will be no doubt that you are anything but fat.