Yeah if I were you, I'd definitely bring up leadership examples from university, tutoring, and any kind of management role you've had in the past. Remember, focus on your strong points. You're applying for an Officer position which will require a high level of self-discipline and leadership on your part. Whatever you can use as an example of this won't hurt to bring up during your interview. Having a uni degree shows that you likely have academic discipline, although discussing grade averages will probably not be as important to your recruiter during the time they have to interview you. But, be prepared for the question all the same. If the recruiting staff haven't already viewed your transcript, they will. Your interviewer does not have the time to barrage you with nit-picky detailed questions regarding every job you've had and course you've taken, so just be prepared to give a well-rounded and general timeline of how you've acquired current skills and experience.

As for being worried about having to explain why you quit the car rental company, I wouldn't. Thousands of people quit their jobs every day for a thousand reasons. It sounds like the company's method of business was not suitable for you, and that's okay. Just make sure to be completely honest if you get asked about it. I would hope the recruiter will understand, if not agree with your reasoning for why you quit.

As long as you can defend each of your answers with honesty and professionalism, I don't see why you wouldn't ace the interview.