How to Bounce Back from Missed Opportunity

I was at an event yesterday and saw a girl who was literally exactly my type in this green and white sun dress. She started talking about an interest she has which is one I share and not common in women. Idk if she or her friend caught me checking her out but she started standing really close to me, maybe she wanted me to say hi idk. I've always been to shy to talk to strangers, especially women and I have no idea how to strike up a conversation even though I had so many things on my side in this case. I've had this sort of thing before but I've never left the situation kicking myself so hard before. How do I bounce back and build the confidence to shoot my shot?