You lack confidence because you lack knowing Allah properly. You have to learn more about Allah. Reciting the Quran daily helps but it is not enough because you have to understand what you are reading.
If you know Allah, you will have the confidence you need because you know that Allah is with you and that He is protecting you.
You have to learn His beautiful attributes and know what they mean. You have to learn the meanings of the Quran through reading a small portion every day. This way, you will learn what Allah has rewarded His servants who obeyed Him and how He punished those who didn’t.
You have to train yourself to be confidant and that no one matters on earth as you know yourself and you don’t care what others say about you. If they don’t pay any attention to your feelings, why should you feel embarrassed or stressed when you are around them?
Try to associate yourself with a small group of new friends, one or two so that you get out of you comfort zone and start mixing with other girls.
Through this, in sha’ Allah you will progress