Is the way I play this straight costing me money?

[The_Bends]

I think you playee it fine although I would bet more on the river. One thing to consider is that at these minute stakes people are more concerned about the money amount than they are the bet in relation to the pot. It seems strange to say it but people who play 10/20 see only in terms of the % of th epot bet, even though they are betting large sums of money while people at lower limits often think along the lines of 'its only another buck' and the suchlike. The upshot of this is that you can often get away with overbetting the pot particually in the flop when the money is small. Because of the expinational nature of NL poker this should ensure that by the river you have a few more people locked in and can make a few more dollars.

That said you'll have to judge if this works on your table, if people are constantly folding the flop overbets then you'll have to stop doing it.