This happens a lot. You want a nice clean outline like the one on the right, but instead your drawing looks more like the one on the left:
First, let’s take a look at why this happens. You can see that it’s the geometry of the different shapes overlapping that’s causing this:
There’s a few different ways to fix this. This way is the simplest:
As you can see, this is one closed shape (the black outline) with each inner line segment done as a separate stroke. This works well! But it’s only ideal if you want a single solid background color.
There’s another way to do this, if you want each shape to have its own background color. First, open your Strokes panel (Window–>Strokes). Now, round all the corners, as shown:
No spikes, and each triangle is still a separate closed shape. However, the outer corners now look rounded. To fix this add a separate outer hexagon, as shown in the first example.
Sharp corners all around!