If you deliver your opening line to the girl knowing you have plenty to say afterwards (until you introduce yourself) you will be much more confident in both your initial approach and your opening line.
Now don't get the wrong idea here. We do not mean you have to ramble on at length before you introduce yourself. It should be a very short speech, at most 10-20 seconds. Sometimes it will not be necessary at all; it all depends on the girl's reaction. In many cases she will respond immediately to your opening line, in a friendly, warm way. You should then introduce yourself immediately. We are concerned more with the occasion where the girl is a little hesitant. You should only continue with the "filler" until she seems to be accepting the idea of meeting you.
Really! Talk, talk, talk. Keep talking. That's what it's all about. So have your ammunition ready.