Hey [Classmate's Name],
I just wanted to reach out and sincerely apologize for how I spoke to you. I never intended to upset you, and I realize now that my words came across the wrong way. It wasn’t something personal, but I completely understand why it might have felt that way.
I truly value our friendship and would really appreciate it if you considered rejoining the group chat. It wouldn't be the same without you, and I hope we can move