If you are concerned about the readings, I would remove it and start a new one. From my past experience Abbott were always good about replacing sensors that had failed early.
Obviously, you don't know how long under the sensor that it bled for and the blood would have pooled under the sensor which is probably why it looks as terrible as it does as it had nowhere to escape to except under your skin. I've had many bruises like this, some from sensors some from accidents and mine always take upwards of a month to properly heal but my healing has always been extremely slow, it can differ from person to person.