There are few errors or typos. You have proofread carefully and run your spell checker. All three of your major projects are reader-ready. Reports are in correct format and addressed to your client. Manuals are formatted and bound in the form in which readers would actually use them.
Websites are on a web server.
People who get a B in this class have produced good solid technical writing and accomplished a lot in the class. They usually have met some of the above criteria. You may have three good solid projects but none of the three stands out. The projects are usually less ambitious and have more editing problems. One or more of your projects is not ready to be used by readers.