What to do with my ABRASION??? HELP!?

yesterday, i fell off a hurdle and got a pretty bad scrape. i think it's an abrasion. there were white things( white blood cells?) then i washed it. then i put a plaster on. then i changed the plaster every hour and cleared excess blood. It's not a major one, coz it's like 2 cm. now the blood is still not dried and a piece of skin on it is purplish black. WHAT"S THAT? i am pretty sure i don't have an infection. coz i dont have a fever or anything now. i don't feel much pain when i walk or run. i know it's swelling slightly. BUT WHAT"S THAT BLACK SKIN? is it bad? must i see a doctor?