I agree with Soma. I was in a situation once where the teacher liked what I had written, but questioned its integrity. What I did was explain what I wrote to her, how I came up with the design and formation of what I wrote, and explained the ins and outs of the information, demonstrating that I knew what I was talking about.
Depending on the nature of the assignment, show the teacher your sources of information, and describe how and why you put your information in the format that you did.
This creates credence multiple ways. It demonstrates that you know the information, you can describe how you formed and linked everything together in writing the paper, and why you decided to present the information in the matter in which you did. By that point, the matter was resolved and the teacher accepted that this was indeed my work. It should be in your case as well.
But before you go up to the teacher, say a silent prayer to yourself and try to stay clear-headed. Come into it with the mindset of wanting to clear yourself, but also realize that the teacher is just doing their job. They're supposed to question and protect integrity. Not saying that you're not, or won't. But it makes the whole process a lot easier if you meet with them calm and relaxed; and adds to your overall effectiveness and demonstrates your professionalism. And of course, it also makes it easier to present and accept your side of the story. Again, I'm not saying that you won't or haven't considered that. But just wanted to add it in since it helped me.
I'm sure it'll work out in your favor. You wrote the paper, and you did nothing wrong. And of course God's there in the midst, working on your behalf. This situation is just a future testimony!
Hopefully this helps.