A wet Mister Clean Magic Eraser rubbed onto the scratch area, then some rubbing compound polished in with an old cotton sock, then some wax will probably make the scratch much less noticable.
For your knee, soak in a tub with epsom salt in the water, take some ibuprofen, and slowly walk as much as is comfortable to keep the muscles and tendons around your knee stretched out and not getting weaker from lack of use. You may want to go to a pharmacy and buy a knee brace. An ice pack is probably a good idea for the first couple of days, to speed the blood flow to your knee and reduce the amount of bruising and swelling. If you limp for several days, it might be best to see a knee expert.
I wear dirt bike shin and knee guards, and a dirt bike kidney belt while street riding. I had a cast on one leg for 3 months when I was 16 years old, from not seeing a leaning fence post hidden in some tall grass, and breaking my two lower right leg bones on this old abandoned fence post while riding a dirt bike.