My lawyer said to me that she personally hasn't seen anyone facing severe consequences for working for 2-3 weeks during the transitional period between studies and PGWP provided no misrepresentation is involved. By declaring it I mean indicating it on the IMM5710 form, which has a section asking applicants to declare any unauthorised work or study. If it is not declared, it will be considered misrepresentation if found out by IRCC. I don't think your 2-3 week's accidental unauthorised work is a big deal, but you may want to check if your agent has declared it on that form.
Having said that, it is unlikely IRCC will do a close check on your file as they have no reason to do so.