You do not need to use your files from previous activities to continue. You can always download the new files which are attached to activities and just do the specific activity - do not worry if previous activities are not included in the file.
The goal is, that you practice and you understand what we are doing and why we are doing it. Once you understand, than you can move to the next activity. It is not required doing everything for the whole board - that would be a lot of work and it would require a lot of time (some people do it, that is like wow!).
PS: Schematic & PCB Design course is a little bit specific, as it was my first course and I had to use third party design (with their approval, but I had to remove some things and also they did not included everything - very good example to learn
) - in the other courses the files for activities are more complete as they are all our designs.