Wanted to emphasize a few points that I don't think came through on previous posts.
1. Yes, you can enroll in a ROTC program without a scholarship. The enrollment process varies by the unit, so you would need to cotact the unit to make that happen. If possible, I would do that before the start of freshman year since there is often a ROTC orientation that starts prior to the start of the academic year. Again, that varies by unit.
2. You can only enroll in a ROTC program at a college that has a ROTC unit. Each service has an online list of the colleges that have a unit for their respective service. Some colleges only have one ROTC program, some have all three. I'm pretty sure that you will find ROTC is only available at a 4 year college, although they may have an affiliate relationship with a nearby community college. If I'm wrong on that point, I'm quite certain the the number of community colleges with a ROTC program is extremely low.
3. Each ROTC program has a 2 year "screen" in it's process for people who are enrolled without the scholarship and some even for those with a scholarship. For example, AFROTC has Summer Field Training between sophomore and junior years. Participants must be selected to attend SFT, regardless of scholarship status. If you are not selected or do not complete SFT successfully, then you are out of the program. The percentage who are NOT selected varies from year to year depending on the needs of the service. Army and Navy have their own process so determine who, without a scholarship, can move to the advanced program during their junior year and senior years.
4. Anyone in ROTC with a scholarship can participate during their freshman year without service obligation. Even though they are on scholarship, they can drop from the program during their freshman year without repayment of the monies, or serving on active duty. Students without the scholarship will "contract" between their sophomore and junior years and have no service "obligation" until they do so. Even if they drop the program afterwards, there is nothing to repay, since they received no tuition money.
5. I see no advantage to winning a scholarship but not accepting it. You have freshman year as a freebee to decide if the military life is for you. One ought to be able to make that decision in the time allotted.
6. There is no advantage to NOT applying for a scholarship. You cannot win a scholarship if you don't apply.
Hope this is helpful as a 30,000 foot view of the programs. You can certainly learn more by reviewing the online web sites for each ROTC program. Good luck!