Put in wrong ATF, now what?

The sales person looked up the atf requirments for my 1997 Millenia and said dexron III. Me bad, I had not checked it in a long time and it did not touch the bottom of the dipstick. So I put in the quart and now get a reading but when I read the manual it says to use dexron II. How much damage will I do if I do not do an atf flush? And driving it with low fluid for God knows how long. It's not my fault, they really hid the dipstick with no yellow top.

you cant get dex 2 anymore it has been superseeded to 3.   you should put in a bottle of lubegard.  i use it all the time.  

Thank You Keninn, I will sleep better tonight. I know it is my imagination but it seems to shift smoother when it is at the correct level, not a quart low. I think I may have a very slow leak where the cooler lines connect to the radiator.
HAPPY THANKSGIVING TO ALL!