Take A Chance
OP. You have probably already answered your own questions/fears.
Go for it!
No idea about what your scholarship chances are as don't know your ranking in Oz. But if you are top 6 in your state and top 25 in the country then go and do it. You will learn so much about life after 1 year in the US that it will be the best "gap" year you could spend.
You can do exercise science at a US Uni and as long as you pick the right one you will get the credits for the courses you take.
The experience playing on a team, working on your game/good daily coaching & training partners will improve your game.
Your teammates can become lifelong friends & the experience is unique from anything you can do in Oz.
This from someone who decided not to go on a tennis scholarship many years ago...I took every other chance after that to forward my career in tennis. I don't regret not going because of my circumstances then but I have since coached several players who have learnt so much from the experience.