As the name suggests, the ethnicity estimate gives you an approximation of your ethnic background. Here are some of the possible reasons why your ethnicity results might not seem accurate: 

1. You get the best estimate currently possible based on our data and models. But because of continual improvements and new scientific discoveries, your ethnicity estimate might change over time. 
2. Even if your ancestors originate from a certain country, there might have been genetic influence from other places.
3. You don’t necessarily share common DNA with all your ancestors.