I went through this sorta recently, at first I would only use the bathroom if no one was in there, and was constantly afraid someone would confront me about it. Ok I was read to shout them down with legal defenses but still afraid it would become a issue. Not so much of a issue that I ever bothered to talk to management about it but still.
one sorta reassureing moment came a few weeks after I went full time when a female coworker approched me and said she had some advice for me, turns out her advice was that I should use the ladies room because I might confuse people in the mens room. I told her I had been using the ladies room sense day one of my transision.
Now it took a bit longer before the first time I used a public restroom not at work...and now 6 months later my anxiety over using the bathroom is no higher than it was before I transisioned. so success I guess.
so i guess my advice in short is "just keep doing it, like going out presenting female. At first it will seem scary and difficult but in no time it will get almost boring"
Serena