There’s a few troubleshooting steps you can try here @jinnuo1226 : Running the Relational Database Curriculum in your Browser
Some people have reported that it takes several attempts before it saves. This course is in the middle of the Relational Database certificate, were you able to complete the previous courses and get the checkmark for those?
Did you by chance log out of freeCodeCamp at any point between starting and finishing the course?