I don’t know if the same that applies to me applies for you, but I changed drastically when I was 18. Since then it has been easy for me to make friends. You must learn from the Bible and research, but the most important thing is to apply what you learn and while you learn.
So, the main problem is how to approach others. So let’s apply the teaching: “Treat others as you want them to treat you”. What would you like someone that wants to be your friend to tell you, why not a name, what he/she likes, you could even begin by saying “We’ll see each other for the rest of the year so I wondered about xyz”, share your interests, aspirations, what you like the most, what they think is fun, etc. Do with others as you would like them to do with you. I think it’s preferible to introduce yourself to the one’s closer to you in school or to guys, then you can even present your friends to other friends saying someting you know about them.
What comes out of your mouth shows what’s in your heart. People won’t like someone who is sad, so try your best, and if you fail, try better, even ask if you made a mistake if possible, or from help if you do something bad, as a humble person would. Even if you try your best there are people that won’t accept you. But that is not your fault, there’s always people like that and is not easy to know why, maybe they are treated similarly. We are like you, we have the same problems, like many of the same things, wish for the same happiness, have the same needs, don’t think they don’t like you or that they won’t accept you without trying. Act as you wish a best friend should act, and if you fail, apologize and try again.
You can also meet people by helping when someone needs help. In the worst case scenario, people could be indifferent and then for that while there is still someone that loves you and won’t treat you bad ever, and that is God. However, God is the strongest, most important being in the universe, so His friendship is worth any time you have to wait for anything, because He is your eternity and the real source of happiness.
Each teaching you find will help you, and if you want better friends, look for them in places they can be found.
God bless