Talk to one of the LT's at whatever NROTC unit you're thinking about going to and find out what he recommends and when the scholarship deadlines are, and your options for joining your freshman year without a scholarship. Heck, I joined up (CP) my first day at Ohio State. If you get a scholarship (and it may be less than a four-year), it will require some higher math, so be ready for that. Otherwise, being in NROTC is not very demanding academically or physically. You're not PT-ing every day, although I suppose different units can have different PT programs going on. You will, I believe, be required to pass the regular PT standards. You even mentioning "advanced PE" in your post worries me, but as long as you run a bit, do some situps and pushups, the unit should be able to do the rest of the work and get you to where you need to be.
For the most part, you're a regular student who drills after school once a week, has an extra class to take every quarter/semester, and has other commitments (NROTC clubs/obligations), and also will have some or all summers dedicated to cruise-type activities. Other than that, you are a regular student, with the caveat that ultimately, you're accountable to your unit. So behave accordingly.
I don't know what your grades are like, but be prepared to keep a decent gpa--I believe the scholarships require a min to keep them. And usually if you fail or withdraw from a class, you may find yourself in NROTC study hall every day, if your unit has one of those. But generally speaking, IMO, ROTC is the absolute easiest and most painless way of getting a commission.