The figure below represents the present problem:
After we draw the three given points and connect them, we have a triangle.
Then, we pick the middle point of each side, and we draw a line that goes from there until the opposite vertice. Once we do it for the three sides, we will find a position right in the center where these lines cross each other.
This is the circumcenter of the triangle.
From the drawing you sent, we have the following correction:
