Compass calibration cylinder not sphere

I’m using an apm 2.6 board with an internal compass.i tried to calibrate the compass but the shape after calibration looks like a cylinder and not a sphere.The problem is there are edges forming and not curves

Calibrate it away from any metalic structures

Thank you for the reply.
I bought a external compass with gps but mission planner is not showing dots. I soldered the sDA and SCL points ,removed the jp1