Don't beat yourself up too much man. You're social skills are just a little rusty - you're not used to coming up with a load of spontaneous conversation with an attractive girl.

Your problem is purely one of practice, and progressive desensitization. Seriously, all your problems can be overcome by practicing and talking to more girls. So to start:

1. Don't beat yourself up, it wasn't your fault, you're just a little rusty
2. Start talking to more girls and learning to be spontaneous in conversation
3. Learn to master your fear

I wrote a detailed article with an action plan about this here - http://howtogetagirl.biz/start-here/confidence/

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How to Get a Girl - www.howtogetagirl.biz/

Mate I'm struggling with the same thing, you're not alone.
What everyone else said is spot on