I will do the best to simply things for you. If one commits a venial sin and dies before confessing it, one would not go straight to hell, but would have to spend time in purgatory before entering heaven. These categories do not exist in the Orthodox Church. Sin is sin. When we miss this mark, when we fail to hit this target, we sin.
Murder is a sin.
Pride and envy are sins. Stealing a car is a sin. Stealing a candy bar is a sin. Missing the mark is missing the mark . If we aim at the bullseye and miss, it makes no difference if it is by an inch or a yard.