Great job starting young. While you do have the leeway to take a riskier investment approach, I would still focus on proven, stable investments for a while until you learn more about investing in small-cap stocks or growth stocks.
With that in mind, don't worry too much about whether you missed a stock by a few weeks. You should be looking long term, and in the long run a few percentage points just won't matter. When I was just starting out, I looked at a 5-10 year window that I would hold stocks unless something drastic happened. It's worked out well for me so far.
Look for stocks that provide dividends, especially if they look cheap. With only $1000, you don't want to be trading too much, so a direct investment plan would be a perfect fit. Check out
http://www.dripinvesting.org/drips.htm for some good info.
Once you have some money ($5k or so) in some good proven companies or maybe an exchange traded fund or two, and have spent some time learning about how to read financial statements and do some number crunching, you can think about putting the next $1-2k in some riskier plays. That way you have a steadily growing portfolio with the possibilities of some really big gainers. Use Scottrade or something like that to get low commissions and start looking at 1 year time frames for those picks.