This looks like a burn of your BP. The medication your vet gave you should be OK for now. If its still no good, a culture of the skin lesion should require to determine which antibiotic is the best one to use. In addition, a soak in a povidine iodine solution/Nolvasan (chlorhexidine) for 30 min per day before applying polysporin will be helpful. In severe case, 2-4 weeks of injectable antibiotics and 4-6 weeks of polysporin may require.
Another thing is that burns heal slowly. It may takes a few skin sheds to heal completely. During these skin sheds, you may still see raw tissue; but when the skin grows it should get smaller and smaller until heal up completely. Good luck to your BP!