From your post & comment, my understanding is that both of you worked on the questions together (i.e. you didn't just copy her answers without understanding how she got there) and to the best of your knowledge, there's no rule prohibiting students from helping one another with assignments.
If that's the case, I would recommend contacting the lecturer (or their assistant, depending on how the course is run) and explain the situation to them, and offer to redo your assignment with the correct questions. Make it clear that you didn't simply copy from work that your friend did, and that neither of you were aware of any rule against helping one another with assignments.
If you don't do this, there is a risk that they will notice the identical answers and assume that you copied from your friend. Depending on university policy, there may also be consequences for your friend if they assume that she let you copy. Even if neither of those things happen, you probably won't get a good grade for the assignment if you answered the wrong questions.
If there is a rule against collaborating on assignments... there may be some consequences, but it's going to look a lot better for you if you come forward instead of waiting for them to notice.