For the people talking about Josy being more into MC than Maya at this stage, I have to say that I agree. She asked MC directions to go to his dorm and Maya acted very surprised when she saw who was at her door. So we can easily conclude that Maya was not expecting her, and that Josy was there for MC and not Maya, even if she would have gone to her at some point later.
I think she was quite surprised when Maya opened the door for her. Poor thing, I bet she meant to reveal everything to him as soon as she had arrived, and maybe even had made up her mind with a decision about what to do next. Looking at the bags in her hands, I would say she had chosen to stay with MC for good.
I don't think it's possible that Josy went to that dorm room to see the MC. When Josy calls him, they have the following conversation:
MC: "I don't know what to say..."
Josy: "You don't have to say anything... ...except... ...tell me your dorm number."
MC: "Why do you ask?"
Josy: "Well, I was thinking... Maybe...until I get my own dorm...I could stay with you?"
At that point there is a choice for the MC to say that he is staying with a girl, or just that he is living with someone and there is no room. Either way Josy responds understandingly and says,
Josy: "I can always stay with a friend or something."
Implying that the 'friend' is Maya. While Josy does ask directions from the MC, he never provides them.
It also seems to me that Josy would have already known where Maya's dorm room was. She may have already contacted Maya to say she was coming. Just not when. I don't really know about that. But she did no where to go, just not from the MC.
So Josy's stunned look was not because Maya opened that door, but because the MC was there, and Josy suddenly realizing that Maya was the person the MC was staying/living with.