There are almost 15 000 000 Google hits for "paint in the edges", eg:
I also paint in the edges of the base at this stage [ – ] it makes the
whole thing look so much tidier when it[']s finished.
This shows that at least one related verb takes the particle / adverb (jury's out on this) 'in', which gives the sense 'add a necessary/desired part of the whole drawing / painting ...'. (Note that 'I also paint the edges of the base at this stage' has a different meaning, unavailable with 'draw'.)
'Draw in' can be used to mean 'add as a required part of the drawing' (eg
Draw in the trees using a dabbing motion with the side of the knife to
create a bark look.
Next, we draw in the flowers and the jug.
from the internet), but perhaps a simple 'added', 'or 'added to the drawing', sounds less junior-school register. Here, 'the plotted points are now connected to show the edges' might work.
A slight complication with 'draw in' is that it has other meanings, as a true multi-word verb. See Macmillan Dictionary. The word 'in' is made to do many jobs in English – it's little wonder people get confused. And it's such a small word!