http://www.goaskalice.columbia.edu/2067.html
One guess is that when you inserted your finger you were just testing and not really exciting or playing with yourself.
If you were, you would have become WET and the area would swell a bit with increased blood tissue flow and you could have fully inserted at least one finger.
http://www.revirgination.net/vaginal-size.html
http://ezinearticles.com/?Is-Your-Vagina-the-Normal-Size?-Ways-to-Tighten-a-Loose-Slack-Vagina&id=1593285
Check out the links and you will discover all is going to be ok - That is IF the guy educates himself and if he does not at least you will be more informed and be able to guide him.