no not overstocked. a good way to know if it is (by common sense) is to see if your water change schedules are good enough to keep the bio readings where it should be and by simply watching your fish's behavior.
if they aren't killing each other and swim around just fine without bumping into each other. its not overstocked.
those 3 things all need to be met. easy and common sense. good thing you got small tetras. shoal away.