You're not planning to take the LSAT anytime soon, are you? I think the score expires after 5 years, so don't take it until maybe your junior year. You'll probably do better then, anyway, as you go through progressively more challenging courses at college (one would hope, anyway).
Hard to say now whether self-prep or a class is what you'll need. Once you take a practice test, you'll see how much help you need. The games section is particularly tough; that and CR are the ones most of us need help with. If you're not great at standardized tests, then a class would probably be worth it to you.
If you go for a class, check out Princeton Review also...a friend of mine took their class and scored in the mid-160s, enough to get into her first choice school. She graduated in May and passed the bar not too long ago! I haven't taken their LSAT class yet but am also waiting to see if their new "hi-test" class (it has more hours) comes to my area.
But for now, relax. You've got time.