Well here is my story:
I arrived as a freshman at the University of Central Florida ( I miss it immensely ) and decided that I wanted to apply for the NROTC scholarship. First off, let me say that you should apply as early as possible. You can take the ACT again if you need to, even if you are in college. Boost your scores and shoot for 29+ in Math and 31+ in Verbal ( I'm not sure of the exact criteria since it was two years ago) but score well and you can be selected in the Early Decision program. Call your NROTC advisor and ask about it because they don't normally advertise it. They like to use it to select their women and minority candidates, so if you're one of those even better, I wasn't and I still got selected. I retook the ACT and got my qualifying scores before I got to UCF and completed the application. You can send in your college grades after the first semester ( if you don't get an early decision) and they can boost your application status. Also, when picking schools, pick wisely. I've been told that it is easier to get a scholarship to a state school with in-state tuition vs. somewhere that costs $40,000 a year. ( Could be bad gouge, but my NROTC Coordinator told me it was true). If you get awarded a scholarship don't slack off. My coordinator had me send in my final transcripts and threatened to take away the scholarship if I didn't have at least a 3.0 GPA. All-in-all you don't have to already be in the university to apply for the scholarship, so go ahead and start! Don't get involved in the NROTC program on-campus because you won't be allowed to apply nationally and participate in the program. It is either one or the other. It is awfully competitive to pick up a scholarship once you are in the program and the best deal is to get one nationally! Good luck and feel free to ask anymore questions!
One last thing I didn't address, you will still submit high school transcripts and activities!