This happened/happens to me a lot unless I 'm really attracted to the girl. The "counter-intuitive" thing is this raises interest like crazy and usually they'll come and throw themselves at me a week or so later. Weird. Or so I used to think...
I could talk to any woman I wasn't attracted to. Charming, funny, relaxed. Then a gorgeous woman looked my way and I'd become a sweating, babbling mess.
The fix took me years to find and ten minutes to learn. Nervousness and excitement are the same physical state — pounding heart, adrenaline, flushed face. Your brain just picks the label. And you can pick a better one.
Rule 16 shows you how. You feel the nerves, relabel them as excitement, and let that energy pour out as enthusiasm. Women notice the guy radiating it. They always do.