Yes, tou can ask the judge for an early termination of your probation under these circumstances. There is no guarantee that your request will be granted because part of the reason for probation's that you remain law-abiding for a specific period of time. The fact that you have hastened your probationary obligations bodes well for you. Good luck!
I agree with the other answers. Six months is a very short time for probation, and it is a very short time as well for demonstrating what probation is supposedly all about -- Proving that you have 'learned your lesson and won't offend again.' You can try to get expungment early, but I doubt the court will agree. Perhaps it would be best to wait out the six months and then file.
Best wishes for future success.
Although I am an experienced CA criminal defense and appeals attorney, I can not 'guarantee' that my answer is entirely accurate, since I have not reviewed all of the factual circumstances of the case, nor have I discussed those circumstances fully with the questioner. The fact that I have answered this question does not establish an attorney client relationship between the questioner and my self or my office.