It’s not at all unusual for teens to worry excessively about what others think of them. It is not unusual for teens to be self-conscious in social situations or to be shy. It is unusual to think that others are reading your mind. I can’t tell from a letter whether you are a normal kid overthinking your shyness or if you may perhaps be struggling with something like obsessive compulsive disorder. (It’s unlikely that this is psychotic thinking because you do realize that your thoughts about other people reading your mind are irrational.) Whatever the cause, the thoughts are getting in your way and are causing you to suffer much too much.
For that reason, I strongly urge you to make an appointment with a mental health counselor. A counselor can hear your whole story and can work with you to sort out whether you simply need some reassurance or if you need some treatment. Bring your letter and this response with you to your first appointment. It will help jumpstart the session.
I wish you well.