If you seriously want to be competitive for top scholarships, you probably should put quite a bit of effort into ACT prep. Yes, you are only in 10th grade, but realistically, there are plenty of kids that are scoring significantly higher than that in middle school for the different talent searches. http://cty.jhu.edu/summer/docs/intensive_eligibility.pdf Those are the kids you will be competing against.
But, you have great instate options that are affordable. And like @irlandaise pointed out, there are top students to be found at publics. Our very high performing son is a freshman at UA and loves it.