You haven't done anything wrong, welcome to the world of Stilton (scary ain't it)Take a look at some of the ones on the forum.
Hey! It looks very good... :-)
Looking good!! The aspect ratio of height to diameter is good as is the bluing. The blue typically shows up on the 5th day and grows from there. Depending upon which strain you use it will grow fast or slow. I use PV and it grows rather quickly. Looks like you're right on track for an excellent stilton. I would consider cutting into it at 7 weeks. Also be sure and let it air out at room temp for about an hour a day. That way your rind will develop naturally.