As someone who has struggled with self-esteem issues, and social anxiety, I’ll tell you what my Muay Thai teacher told me.
The secret of confidence, is this: Confidence is knowledge. Knowledge of a likely result. When you put food in your mouth, you do so confidently because you know from experience that it will nourish you. When you put one foot in front of the other, you do so confidently, because history tells you that that’s a good way to ambulate from one point to another.
Much the same, the only way to be confident in social situations is to experience them. If you want to be confident asking out a boy, or a girl, try asking out boys and girls. See what works. You’ll become confident.
You want to try a new sport? Try the new sport. If you like it, you’ll end up playing confidently, because you’ll know how to play.
Anxiety, uncertainty, fear. These all come from the unknown. Educate yourself. Experiment. Learn. With knowledge will come confidence.