Yeah I totally feel your pain, I started using the female's bathroom before I started HRT, and I mean I use it now still and I am not very passable, I totally look like a "man in a dress". It really comes down to just getting used to it. I wont lie it is still very awkward as hell but I find the more I do it the easier it becomes. But you sound like me, so here is a run down of the worst that could happen, according to my own mind:
Get harassed for using the women's restroom:
1.) Women scream/attack you
2.) Women call their guys to the rescue.
3.) Guy "is the hero" and drags you out of the restroom and declares victory over the "trans invader."
4.) Someone calls the policy and you are escorted out and fined
5.) Women make nasty faces or remarks at you
Get harassed for using the men's restroom:
1.) Attacked or raped because you were "asking for it" coming into the men's restroom, "That's a dude, they knew what they were doing coming in here."
2.) a group of guys perform the violations and harassment found in problem 1 above.
3.) You get murdered or seriously injured.
4.) Gangbang type of murder/rape. Remember; "You asked for it coming in here like this."
5.) Men making nasty faces or remarks at you.
What's the difference here? Generally you will find if the worst happens in a women's restroom, its going to be about making a big scene, about people seeing what is happening and or making sure everyone is aware, so this leaves you embarrassed and humiliated as all hell but people are watching. The other alternative is that men wont make a scene about it, they will just rape or kill you.
Seriously girl, its dangerous for you being in the boy's room. This might sound awkward as hell but try going from store to store where there are public restrooms and just go in and follow the motions (check your facebook while on the toilet) and just get used to it. don't wait for everyone to leave, walk out and wash your hands and check your makeup like you been doing this your whole life. Most women I have been in the bathroom with don't even notice even if I am over 6' tall and built like a football player but in a dress.
I should also mention I live in Idaho, the land of bigotry, and I have yet to have any problems in the 4 months I have been using the ladies' room.