Having made a first pass at a system map, now is the time to test and refine it.
Does it help to answer the kinds of questions that you are trying to answer?
Test it offline with stakeholders and ensure that the dynamics are captured correctly, so that their narratives and your map reinforce each other.
You may need to adjust the boundaries of the system, so that some of what was in the ‘outside world’ is included. And you may need to add or rewrite nodes, or tweak dynamics.
The aim is not to get to a system map that is perfect – just to create something that is good enough to start working with.