It's not you per se. Men are quicker to admit to feelings of love then women are. There was a research on this very subject not too long ago (
http://www.telegraph.co.uk/news/newstopics/howaboutthat/8852761/Men-quickest-to-say-I-love-you.html ).
Anyway, it sucks that she can't return in. 4 months is plenty of time, so I don't think you're too quick with this. In my previous relationship, I was the first as well. I didn't get one back straight away, but it didn't take long. That said, my now ex did say that she didn't expect me to say 'I love you'
that soon.
As for what you should do... I would recommend not letting it show too much. But don't repeat it ever again before she does. There's still a change to shift the powerbalance to equality, but she has to make the move. Just continue as you've been doing and try to not let it show.