Was it a multi-choice question looking for both ? If you are referring to the question that I see pop up when I look at that lesson, the only correct answer is «nous nous assoyons» as all the others have the conjugated verb misspelled. If not one of these, you should report through the quiz issue button to get confirmation of where the problem lies.

I'm not sure. Maybe you made some other mistake (e.g., a typo) in the sentence and that's why it was marked wrong? Can you give the entire sentence?