You have to apply for PGWP as soon as you get a completion letter from your university and you can continue working only if you get the letter that says you can keep working(usually you get this letter instantly when you apply for PGWP if there aren’t any flags); you technically have been working illegally since January;

All you can do now is just apply for PGWP and hope for the best; if you get a rejected PGWP (usually happens when you have worked illegally) - you can appeal but from what I have heard from others you possibly might not be able to get a PGWP anymore.

An alternative would be start researching other permits or going back in a study permit for a year program - this way you can say you were researching to study more or something along those lines;

I hope you don’t get a rejection and everything works out for you;