Will one bear the sin on the Day of Judgment for misleading a non-Muslim, should one prevent him from embracing Islam, and is there repentance for that?

A Muslim must strive to guide disbelievers and invite them to monotheism and to embrace Islam. It is not permissible, legally, to be content with convincing them of the religion's truth without them embracing Islam. You erred by not thinking well of the man and not seriously trying to convince him to embrace Islam. You must repent, contact him again, and try to convince him to embrace Islam, or seek the help of scholars to convince him.