If that happens, it's probably because she's uninterested in you.I find it hard when ask a girl, a phone number, because after a meet, there might be lost contact or some sort.
Another thing I don't like about language exchanges is that there is always people that are better than you whether it is in the language, or anything, career, etc.
I easily get jealous sometimes, and it feels pressure to me to keep up to those standards at the same time.
People might say maybe you just have to compare the people that are no better than you, that would make you feel better.
Maybe I am just babbling here, but at least I get to meet Japanese people in person.