To be honest, your chances are slim to none right now. Too many things going against you - your GPA and GMAT are on the low end (and no, there's no explanation for it because frankly there's enough people who have had similar circumstances who still got higher scores than you did) and you don't have any post-college work experience.
It's in your best interest to go out and get a full-time job for at least 2 years before applying to a top b-school. Even at schools like HBS who are more willing to take fresh college grads, it's basically about a dozen or so out of a class of 900 -- and these people have exceptional academics as well as exceptional leadership experience throughout college. Even at Wharton, the only people you'll see with no post-college experience are the submatrics (the Wharton undergrads who can do a 5th year to get their combined BS/MBA degree - and these kids also have exceptional GPAs).
Also, even if you were to get into b-school right now, you will be looked down upon. You will have a tough time competing with more experienced classmates for post-MBA jobs. You will be simply out of your league professionally, and out of place socially.
When you graduate from Penn, go and get a job, and worry about b-school later.