Which extract, rootbeer? You can test by adding to a bottle of sprite. For a half liter bottle of water, I add a little bit more than the smallest drop I can pour of zatarain rootbeer extract... you can pretty quickly see if it is right by the color, even without shaking.
On the other hand I have several versions of flavor drops that are super concentrated and require much less.
Tripping on carbonic acid, high on fructose!