First: you should be confident. How can I know what my classmates think of you and conclude that they don't like you? From a psychological point of view, it is often a neurotic reaction of one's own, which magnifies the problem and forms a vicious circle over time.

Second: As for how to cultivate self-confidence, there are many ways, which vary from person to person. You can read some books about self-confidence.

Third: communicate more, mainly because it is difficult at first. Once you start, things will be easy. Let go of embarrassing thoughts, treat people and things around you warmly and sincerely, and stick to it for a while and you will form a habit!

Fourth: I recommend you to read Behavioral Psychology and Behavioral Decision-making when you have time. There are many electronic versions on the internet, but I really can't find the opportunity to send them to you. I believe you will benefit a lot from reading these two books!