Nope, If you are contrite (sorry for your sins) when you go to confession, and the priest pronounces the absolution, you are forgiven of the sin(s) you have confessed. If you legitimatly forgot any sins, they too are forgiven. What remains is the penalty due for those sins.
To put it into terms that you may understand better. You go to confession and confess that you stold $100.00 from your mother. The priest absolves you from the sin. You still are required to return the $100.00, and you still have the penance for your sins.
Most Protestant theology teaches that once you say that you accept Jesus as your savior, any sins you have committed in the past, now or in the future are forgiven, and Jesus did penance for you.
As Catholics we beleive that we cannot be forgiven on our own, that it is Jesus, passion and death as well as his rising from the dead that enables us to be forgiven, however we are still responsible to make restitution for our sins, that restitution includes both the temporal restitution, (as in the $100.00 above,) and the offence we have made to God, by rejecting His will. This does not take away from Jesus’ sacrifice, but unites us to His Sacrifice.