If you pled guilty under the first offender's act then you are not convicted of a crime. You can be adjudicated guilty and then stand convicted only if you are brought back before the judge on a probation violation. As far as your record is concerned, the display of the arrest charge will remain and the sentence part will read plead guilty under first offender act. It is not a conviction.
Under First Offender, your adjudication of guilt is withheld and if you successfully complete the first offender then you will be discharged and acquitted. You can legally answer i have not been convicted of a crime. You need to pull your record from GCIC and correct that mistake asap. The arrest should only show now that you are on active probation.