I agree. I actually think it'd be hard to get in with 60 unit gpa of 3.5 or below. That's just my assumption from seeing how competitive it was this year to get in. While volunteering is good, almost everyone I have talked to or met who applied had volunteer experience, so I wouldn't count on it to set you apart from the rest of the applicants. NOT having some community service/volunteer experience might set you apart in a negative way, unless you had interesting employment experiences.
Because CSUF is such a formulaic and grade-heavy application process, my suggestion would be to take lots of units in whatever classes you can be sure to do well in during summer and fall next year. This way you can load the last 60 units in your favor. Also, if you have any prereqs left and you're not absolutely sure that you'll get an A, leave it for Spring. That way it is counted as "in-process" when you apply and it's grade is not added to your GPA calculations. Remember, the prereqs are doubly important because they are counted in both the last-60 and the prereq catagories for the CSUF application equation.
Despite the importance of grades, don't forget to put a lot of time into your letter of intent. The interview process was pretty cursory, so the letter seems to be the only way to really let them know who you are and what is special about you. Also, make sure that the people you ask to write your letters of rec will write you good ones. The prof that did our interviews told us that multiple applicants had NEGATIVE letters of rec sent in for them. That's just ridiculous!
Don't stress the interview. If it's like this year's, it's really more of an informal vetting of the candidates. It could not have given them much to work with besides a sense of 1) does the applicant speak English, 2) are they relatively normal (or can they pretend to be for an hour or so), and 3) is the applicant acutally interested enough to show up on time.
Hope these are useful comments.