I wouldn't worry about it all that much. Personally, Junior year for me was when I really started hanging out with a lot of people. At that point, I got involved in a few things, I was captain of the ski team. Yes, I know it's not the football team, but whatever, it was my thing and it still is really. However, I think the reason Junior year was the year that I came more out of my shell was that I finally had a car. Having a car was pretty much a necessity as it really was quite difficult for people to get together outside of school without transportation, as our school had a pretty vast geographic area, about 10 miles east, west, north and south.
I found out that I was a total gear-head, and hung out with other car guys. Really, with the group of people I hung out with, we weren't the type to take girls to the movies on friday nights, instead you would find us at one of our houses doing work to one of our cars, whether it was tinting the windows, upgrading stereo's, fixing problems, and just the general stuff that teens do to their cars to make them look cooler, that years later we then realize were pretty asinine. Of course, the highly illegal street races at midnight were fun too, and somehow none of us ever got caught which is a miracle in itself.
Really though, don't worry too much, find your thing and find others into it and you'll be fine.