We are unsure what the elements in the attachment are, we assume they are a point in a point series and two annotations. In order to avoid any confusion, you can create a small project that demonstrates this effect so that we can take a look into it.
I can make a blind guess and blame this on the size of the point. It is 10 by 10 by default. When the point needs to be centered at some position X, the point is actually positioned at canvas.left(x-5). Now what happens here is that the point is 5 pixels to the left, one pixel on top of where it should be, and it is 4 pixels to the right. This is where the visual problem occurs - it is 5 pixels to the left and 4 pixels to the right. You can try avoiding this by setting an odd number for the point size, say 11x11.