As noted in this help article -
"More than 90% of freelancers have a score after 5 projects. Since not all projects and clients are equal, the length of time will vary. Nearly all freelancers have scores after completing eight projects. The projects need to be with at least three different clients and take place within a 24-month period."
I would recommend that you continue doing great work on your present and future contracts so that you can get a Job Success Score soon. You may also want to refer to the help article I have linked above for more information about Job Success Scores.