First things first, take a look at your Participation Report by clicking "Track my own participation" under "My Community Stats":
Here you can see your posting history as well as a breakdown of your weekly participation. At the top, you'll see the posting requirements that your professor has set including weekly deadlines and grading parameters.
Make sure that you've completed the correct amount of posts (questions and responses) required before the deadline, and that you've met the Curiosity Score minimum (if there is one needed). You can see the timestamp and Curiosity Score on the bottom left hand corner of any post.
If you still have questions or need further clarification on your grade, please contact your professor with your concerns.