Yes, Turnitin is a paid service but in the past their support was a little disappointing. Although, I have to admit that it has improved in the last year.
In the mean time, I have found a work around for this. I have asked the tutors to add a new grade item and re-enter the marks there. Unfortunately it's quite inconvenient, but at least the marks will be available to the students.
Thanks and Regards,
Naomi