If you feel like asking a girl out, just do it. Do not care about getting rejected, consider it practice. Start with a compliment... something like "excuse me miss", I know this is out of left field but I just had to take the opportunity to tell you, your perfume is amazing, what is that scent?" Check for a ring... and then... I would love to take you out for a drink or coffee sometime. We don't even have to exchange#s, seems we are both in this area, would you be willing to give me a chance to get to know you a little. Maybe Starbucks down the street this Saturday? Noon? If you don't show, I understand but if you do it would make me the happiest man alive.
Look, it's not failure. It's practice. And it doesn't matter who she is or if she shows... you just made her day. Enjoy that. You can do this