Ok, more info on this trade. I bought at 30.75 and sold it later that evening at 30.89, but I think I've been looking at the wrong line in my TD app. The upper left corner shows "Option Buying Power" (which is showing $11,620), but should I ignore that and just keep an eye on "Net Liq and Day Trades" (which is showing $12,241) for my actual account balance? My balance was down near $11,500 after I entered the trade, so it would seem that I did in fact recover the cost of the contract as well as the tiny profit.
I hear lots of folks use ThinkOrSwim 'round these parts.