artman,
I've been in your place. I could go on for a long time, but right now, pick up that phone and call the girl.
She is already pissed off and will give you hard time. That's because she has spent the time since she gave you the number wondering if
she is good enough for you.
Now, don't make lame excuses. Open up, say you are sorry, say you were scared to call such a great girl, tell her that you like her. Be nice and honest. Ask her on a date. She will forgive you. Then come back to finish this post.
You have difficulty communicating with people. This is fine. No matter how you got there, what is important where you want to go from there.
Find someone who you can talk to easily. You say you have this one person. Now, find some common acquaintances. You say that you are not comfortable one on one, try hanging around in a group. You can sit in the corner, smile and listen to people. Gradually you will know enough about them, their life and interests to be able to hold a meaningful conversation. Practice on one or two people, then gradually increase the number of people you let in your circle.
Don't expect everybody to be your best friend. Just know about other people's life. Read their blogs, if they have it. This way, you'll be able to know what's going on in their lives and be in tune.
Try going to some seminars, may be speaking classes, have a social hobby. The shared experience makes it much easier to talk to people.
In no time, you'll have great social skills.
You seem to be an introvert. Introverts are smart usually, so you have a lot of interesting things to say. You don't have to chat a lot, a few well placed comments will make people interested in you.