Your name is Jammie. You're a relatively normal young man, studying to be a game designer in a large city in the northern United States. You're pretty secure in your masculinity, but it's never been a massive part of your identity, you're pansexual, though not super queer looking. You've said before that you wouldn't mind being a girl, and you assume this would prove it.
When you ended up in the station this world caught your attention. It felt like a good way to mix things up. You're not changing everything about your world, but you're still changing enough for it to be noticeable. Being a girl might be cool. And you have an suspicion that things would be slightly better in this world then they were in yourse.
You are a bit nervous, in that way that being nervous tends to blend with excitment. So much is about to change. You are realizing that your last change to back out of this was long ago, and you realize that the feeling of your dick between your legs on the train is the last time you'll ever feel your dick again. You're really realizing that there's no going back.
Suddenly as your heart is racing on the train, you feel the train come to a stop and then wake up in your bed. Your body feels different, without even looking at yourself you can tell you're a girl. You realize your skin feels smoother and softer, and that there's not as much hair as you're used to. You can feel the lack of dick between your legs, it feels so weird not feeling a body part where you used to have one, and stranger still the feeling of breasts on your chest, small ones, but still breasts. You really did it now, it wasn't just a dream, you became a girl.