How do you say: I just realized that..?
I just realized what I have said!
5 Answers
To realize is translated by darse cuenta de que...
To have just uses the construction: acabar de
Update I have just read a correction by a native el gritón I am so sorry to have unintentionally misled you 
but I gave you wrong information
It should have been:
Me dí cuenta de lo que había dicho
= I just realised what I had said
Please ignore the faulty information below These constructions above need to be conjugated for the correct people:
I have just realized what I have said!
= Acabo de darme cuenta de lo que he dicho
I realised what I had said
= Acabé de darme cuenta de lo que hube dicho.
I hope this helps 
Acabo de darme cuenta de que...
this is so wrong: Acabé de darme cuenta de lo que hube dicho means something quite else
It will have to be: Me di cuenta de lo que había dicho if you want to say "I realised what I had said"
Acabé de darme cuenta means: I stopped realising, and hube dicho is practically never used in modern Spanish, but you will find expressions like this in old literature like El Quijote by Cervantes.
Acabo de darme cuenta de lo que he dicho.
Not a native, just musing.
Acabo de darme cuenta de ___
