Perhaps your approach is wrong?
I'm wondering where you're meeting girls who you ask out. For what it's worth, I'd never go out with a random who approaches me in public...so I hope you're not doing that. If I was going to date someone who came to my workplace, I'd want to get some type of rapport going with him before I accepted a date. Most of all, I'd be inclined to date someone who I got to know via friends or sport or a social activity.
Get to know someone well enough to establish their availability. When the two of you are easily able to share some laughs and chatter then ask her out. And back to the girl in the drugstore, I also would avoid someone who told me I was pretty. I want to know that I'm being asked out because we get on so well....not because of my appearance.
Does this help at all?
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.