How did I over fill the transmission?

[JDmills]

Just changed the transmission filter and fluid. owners manual says 6.6 qt of atf for a fluid change. I put in six quarts, started the car, put it in drive (it is on jackstands) then checked the fluid... Way overfilled?? and leaking fluid from the tailshaft I think..

so should I Just pull the drain plug, and let some out? How did I manage to mess this up?
Jason