I don't know about that, Nadir. I always thought that even though your sins HAVE been forgiven, we still have to suffer for the offense we've given to God, either in this world or the next. Yes, it's true that God does "forget" your sins in the sense that past mortal sins that have been absolved through confession won't be held against you at the moment of your death, but you are still accountable for the action.
To the OP, who can say how God will judge your time in Purgatory? There are so many factors besides just the sins you commit! Your faults, your acts of charity, your prayers, state of life, etc are all considered. I would suggest you read the book "Purgatory". It gives an excellent explanation of it, as well as many interesting anecdotes. Actually, I'd recommend every Catholic read it.