Send an apology message to the teacher, but the teacher didn't reply. What a shame. What shall we do? I'm sorry to see him on Sunday!

What's so embarrassing? A few years later, when you go out into the society and look back, that's all. No big deal. Don't be ashamed when you meet your teacher. Say hello and apologize generously, that's all. A teacher won't haggle over every ounce, otherwise he won't be a teacher.