As people around you will start to change pronouns more and more, your brain will too. I don't know where you are in your transition but these changes are gradual.
Even after 3 years I sometimes describe myself by my old name. Usually when I'm feeling a bit lethargic, and low on energy. I don't know if the person you were ever really goes away, it is your history after all, but it fades as you make progress.