All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It does not seem –Allaah Knows best– that you are sinful for obtaining those results. In addition, your group is not sinful for not informing the teacher about their mistake, or for you not informing your teacher about their mistake. The evidence is that your teacher told you: “Do not inform me about those mistakes”.
If you refer to the entire group getting the same result, then this matter is up to the teacher and you do not have anything to do with it.
In addition to this, the final result is generally not based on this evaluation alone.