what jagged line thing are you mentioning? the edges of the outlines? or the line art itself? I can say that the line
art is not jagged, though it looks crooked... can you upload it to other site so we can see its fuul size?
if I want to smoothen the line edge, I usually do the pen tool selection... I select the part I want to remove/smoothen
using the pen tool and I select it... it might be probably the feather your friend is talking about...
stroking paths in lines, although its can also be the most noticeable thing an error can stick to, so it really needs a
nice manipulation to avoid getting those jagged line art... honestly, the line art is a little weird and the spots with
error are clearly visible... but I think this just needs a few more practice then you'll get the technique to it!
:))