Do well on your ACT, and I believe you have a great shot at getting accepted to RHP. Take your time on the essays. I believe that is where you will really be able to let Penny, Diane, and the others at the RHP office know that you have the motivation and capability to do well after skipping your senior year.
I don't really think you have to be "outstanding" in terms of academics to be in RHP. I can't say for sure how much of a chance you have, but I know that each class is very diverse and has a wide range of interests and passions.