Yes. Once you complete pti the court should issue a dismissal order. The charges and any plea are dismissed. Six months from the date of that order you can expunge the records so the record of the arrest is gone from your criminal history.
Bottom line is that you should now have the records of your arrest, plea, and PTI dismissal all removed from public view through an expungement. That is the only mechanism at this point to have the entire event removed from your record. You must wait 6 months after the PTI dismissal before an expungement petition can be filed.
Unfortunately, IMO it depends. If you are a foreign national, the guilty plea and allocuation stand as is. ICE could obtain the transcript and move forward. If you are a USC, no sweat.
If you completed PTI no conviction was ever entered. But the statement you made is a court record and is not "vacated", the plea is vacated and the case is dismissed. As one of my colleagues indicates the INS uses these statements against people. On the other hand the admission is not used to support any charge since the case has been dismissed. You can petition to expunge the arrest six months after the dismissal. The expungement takes about 8 weeks but the figure 8 weeks more for the state police to take down all entries. The PTI stays on the Court's books to make sure only one is ever issued.