be happy you havent done it wrong in this case

what you have is poserfying

thats where poser finds long narrow faces and makes them look relly bad

there is a few ways to fix it but i will give you the easies way

delete the center vertice and then select the ring that is left and extrude it inwards

scale it to about half of the diameter and extrude again and scale it until just before it is 1 vertice diameter

extrude  1 more time and merge at center

resave and pull it into poser and it should be fixed