I’m paying a higher part-time premium when I’ve been working full time

My job offers insurance to part time and full time employees based on your average hours. In 2021 I was changed from full time to part time after being .45 hours short of the average. Part time employees pay 60% of the premium, full time employees pay 40%. The rest is covered by my employer. I have been working full time hours for most of this year but I’m still paying the part time premium. I’ve asked my boss to switch me back to full time. Am I entitled to back pay for the amount I paid while I was working full time? I’m in California.