Suggest Treatment For Knee Back Injury

Hey there! I was out surfing today and got run over, which isn t too uncommon. The fin hit the back of my knee, but instead of a bruise there s a long raised bump. I d say it s raised about a millimeter or two, and three and a half inches long or so. It s red and doesn t look like much aside from that, but it s causing me to limp quite a bit, and hurts if it s moved past a few small angles. It s soft and doesn t hurt unless I press down on it and touch the muscle (?) beneath.