I don't think that the records of an offense treated with a first offender sentence can be expunged. The first offender statute, OCGA Section 42-8-62 has requirements that the record be stamped with language that says that the discharge completely exonerates the defendant, but it also says that "nor shall the contents thereof be expunged or destroyed as a result of the discharge." The good news is that section 63 states that, with some exceptions, a discharge ... is not a conviction . . . and may not be used to disqualify a person in any application for employment or appointment to office in either the public or private sector.
I hope this answers your question and congratulations on successfully completeing your probation.
You will have to wait until your case is completed before you file for an expungement. And then you will need the consent of the DA's office in order for your case to proceed. Good Luck!