I totally suggest the Junior College route, even if you have the grades. I spent more time in High School causing trouble than doing homework so I went to the Community College majoring in Anthro. I'm a Sustainable Agriculture major at UC Berkeley now. In my opinion when you are 18, you have no clue want you want to do, and a Junior College lets you 'shop' around a bit without the competative and rigid curriculum. That and it's cheaper, especially if you get you fees waived. UCs like transfer students, Berkeley loves them, we are held at a higher standard.
Don't fret over your grades to much, I got mostly Cs (due to my contempt of the scoring system where hmwk was worth more than tests), and when I transferred to Berkeley I only had a 3.4, I wasn't in any clubs or organizations. Learn what you what to learn, find something outside of school that interests you and study the hell out of it. I went on every Geology Field Trip in Community College, not because I was going to major in it, but because I liked it and the experiences I gained from it. The focus on grades detracts from experiencing what could be out there for you (that is meant in a completely non-paranoid way).