College ROTC & acceptance questions?

I was wondering if you could take ROTC in college just by selecting it or if you had to be chosen. Like when I'm selecting my courses would I be able to put down ROTC? Or would I have to send in an application and hope to get picked if I don't get a scholarship?

I wanted to get a degree in criminal justice and minor in military science and hopefully become a special investigation officer or an intelligence officer.

I want to attend a Army or Air Force ROTC college but I'm not so sure if my grades will allow me to get a scholarship. I have a 3.5GPA I'm not taking any AP or Honors and I play soccer and really the only leadership position I hold is Corps Commander at my AFJROTC high school. But I have been in the local newspaper and the news for my work at volunteering and donating that was acknowledged. I'm not sure if that'll help.. Also, I haven't been offically tested but I can do 30 push ups in a minute, 60 sit ups in a minute and can run 1.5 miles in under 9 minutes and I can do about 6-8 pull ups. But what do you think my chance of getting a scholarship would be