For the few specs you gave in your question, it appears you didn't really overpay. That area has been up-and-coming over the last couple of years and if you are going to be there for the next 5-7 years, then you should be able to make a profit if/when you sell it. I have a client with a house in Petworth, with the same specs you mentioned, who will soon be listing slightly higher than what you paid and that's low for his neighborhood because he wants a quick sale. The DC market has never been as bad as the rest of the country since the bubble burst and, in fact, since January prices have been inching upward and we have even been seeing bidding wars again.
I believe you have made a good investment in the future and will find that, even if you did slightly overpay, it will be worth it in the long run.
Welcome to homeownership!
I specialize in Capitol Hill, but I work a lot in the rest of DC (and only in DC). Are you south of the Georgia Petworth Ave Metro? West of Sherman Ave? If so, you are most likely just fine. Petworth is a location that has taken a big hit - it is the location in NW that arguably had the highest foreclosure rate. However, most of that inventory were homes that hadn't been updated. And they are clustered closer to Brightwood (i.e. north of Emerson St NW). I can site 4 comps that sold in Petworth near the metro at 599K with the same stats you provided above (on - 2 on 11th, and 2 on NewHampshire). Additionally, the effects of Columbia Hts is really moving north putting pressure on Petworth, even as developement around Petworth is also growing. My assessment is that Petworth will be one of the "bohemian" centers of the city as it is attracting artists, and independantly owned businesses.
Best of Luck,