When it comes to OG numbers on extract brews, don't let the hydometer fool you: If you added all the recipe fermentables and topped off to the right volume, your numbers will be what the recipe says they should be. OG readings are often skewed because of insufficient mixing of the top-off water. This means you can get a "too-thin" or "too-thick" (look at that scientific leetspeak) reading quite easily, even though your number is right where it should be.
Just a quick-tip quickie as it may help take some of the worry out of extract brewing. AllGrain is where you'll really start to worry about hitting your numbers, if/when you make that transition. Cheers! and welcome to the obsession!