My knee is swollen and bruised on the lower kneecap i fell rollerblading its been a week and its still swollen and bruised it hurts to extend it im 13 years old whats wrong?

It is going to take a few weeks for the swelling to go down. Go see a doctor to have an x-ray and a MRI done to make sure that you did not tear anything in your knee. I also hurt my knee cap a month ago. I went to the doctor and he said it will take a few weeks for the swelling to go down. In two more weeks I have to go to physical therapy. Get well soon. Keep your leg on a pillow to rest it.