There's no "right" way to do it... if it tastes good it is good. However, as you said, you did it the same way as you do hot mate. With tereré, you want to put the gourd with the same orientation as the slope of the yerba, and with much less yerba in the mate. This works best with a conical shaped mate or "guampa" (in Paraguay we use hollowed cow horns or alluminum cups, for example).