Even if you intend to do a karma it is deposited. The desire of performing a karma is considered equivalent to doing the karma. The balancing also is automatic. Once you undo a karma it is removed. In this account a good karma does not cancel out a bad karma.
All karma have to burn out.
We will get into the details of karma later on since the samskara can not be understood independent of the concept of karma. They are closely related. The main thing that has to be understood is that the goal of the samskara deposit is to get to a zero balance. The understanding of this principle is important. Buddha was walking along.