Help creating a 2D interface
 

Hello, I am having issues to create the interface between different zones, I think that my mistake comes from the geometry modeling but I am not too sure about that, this is what I do:
-I create the main geometry (rectangular shape with 2 holes at the middle)
-Now I create 2 new circles (they are a offset of the holes in the middle)
-I use the lines from sketch option
-I project those lines

This procedure gives me 3 faces, but I am not sure that I am doing it the right way, please some help.