Everyone is accountable and responsible for his own sins?

This is part of the fairness of God. No one will carry another person's sins and there is God who in the end on Judgement Day we will be accountable to Him and who willl compare our good deeds with our sins and see where the equation ends to see whether we deserve Heaven or Hell. So how can Jesus pbuh die for us. This is a green light for people to sin as they wish since Jesus already died for us so we are forgiven. What type of fairness is this. So he wasted his life and according to christians was tortured to save people some of which do not deserve to be saved from their sins. Oh no! You want to be saved work on it and act properly. Otherwsie when you sin why do you ask for forgiveness if in your mind you are already forgiven since Jesus died for your sins. Can someone explain this dilemma.