You are a great applicant. You’re already into two excellent safety schools, both great places for premeds wanting to do research. While I can certainly understand why you would have ED’d to Penn, now there is no reason for you to ED2 to Wash U unless you love it much, much more than any of the other schools on your list. Do you? Then go ahead and ED2. But don’t do it to try to play the game of thinking that you’d get in there ED2 and not RD, and that at least you’d have someplace that you might prefer to Pitt or Stonybrook.
BTW, all that’s gonna matter when you apply to med school is going to be your GPA, your MCAT, your research, and the appropriate ECs. It won’t make a difference if you’re applying from Stonybrook or Pitt, or from a more selective college.