3/16" is between 1/8" and 1/4". Once you get used to cutting the seam allowance, you will be able to eyeball it without using a ruler.
The white background is showing: to correct this, the background would be neatly cut away wherein only the seam allowance would shadow.
This is also true when selecting fabric for backing, particularly when using a thin batting: Choose a fabric that is no darker than the lightest fabric on the top.
Suz