normally 4 qts will drain from the drain pan. there about 8 quarts inside the transmission, but you can only change those with a transmission flush. there are several threads about it in the FAQ
Take a picture of the drain plug you removed, and where you re-filled.
You may be two qts low. And that's why you only got 2qts
When I was having tranny trouble a few weeks ago, I drained and filled twice at intervals and both times I got about 5 litres from the trans. pan.
Having the proper level of ATF is very important.
My biggest pet peeve on these rigs is the whimpy trans dip stick. I was always afraid each check I made, it was going to break in two.