Is this Gangrene? Or wtf is going on with my skin right next to a large open wound.?

Hi it sounds like you had a good infection in your leg. Did they make sure that there wasn't anything in the wound? The purplish could be from the bruising you caused from hitting it so hard. Keeping it clean and dressed as you are is good. A wound that big takes a long time to heal and there might be some skin that was torn that will slough off as it died. The Dr. I am sure put you on antibiotics for quite a few days. Take them exactly as prescribed at the same time of day. Keep on cleansing the area. I would wash it with an antibacterial soap and water before dressing it every time unless the Dr. has said otherwise. If it continues to be reddened, warm to touch or starts to drain you should see your Dr. again. Good Luck.