I would definitely talk to your PD and this might involve speaking with the dean of GME. At the institutions I've been to, residents have to pass Step 3 before they can become PGY3 residents. I would figure out how/why you failed and try to address it asap. If you simply didn't study for the exam, it is probably worth taking it soon so that you do not delay graduation. Depending on your fellowship, this may not prevent you from matching entirely but it will probably impact where you would be able to match. This would be especially true if you have had a history of failing USMLE exams or had to repeat parts of medical school.