Well i'm assuming you've already submitted your 2nd app. Keep working hard to improve your app, then send documentation to the school before your interview. Dont let up between now and interview day. Send them everything you've done new and different since you submitted your app. Recommendations, better grades, awards...whatever you can get to make your app thicker and bigger. Interviews start on sept 1, so you got a little over 2.5 months until then, so do what you can to improve your app. Dont let up.
After the interview, follow up with a thank you letter (short and sweet) and emphasis the new stuff you've done during the summer. GL 🙂
Oh and dont freak out, you'll get in...if you're willing to work hard for it 🙂