USC Says:
I.B. Credits:
Six (6) elective units apiece are earned for scores of five (5) or above on high-level exams;
or
Twenty (20) elective units if you earn the I.B. diploma with a score of 30 or higher. General Education credit is available for some history and science exams.
So you can get credit for your HLs. As long as your grades are good, I think you are okay.