I don't think it would be an ethical issue because it didn't offend the guidance. It was all about how your team wanted to do it. I used to do one assignment for 8 people right before the due date, do you believe it or not. If you didn't stand up to correct the errors other people made, you most likely would end up with a fail mark not an A. Considering some people won't let you know until the last minute that he/she screwed, you have to be the life saver sometimes. And this is to show your risk mitigation skills. None of you MBA classmates is fool. They will see and appreciate what you did to benefit the team. But be careful to communicate effectively to people your intention, your approach and the results in a good way without being arrogant.