I have a coupl eof M. roczekii plants, one which I grew from seed and another on a graft. The one from seed is reasonably round, but the grafted one has bigger and longer stems.
Sometimes nurseries graft difficult or rarer species from small seedlings and then take off the graft and root htme down, so they can they sell as "own roots" which tends to command a higher price. It is possible that your plant has come from this kind of cultivation. Hopefully given a bit of time and good light, it will become a more typical shape.
But the heads will get longer as the plant ages. It is, after all, just a variety of M. saboe, whose smaller heads do elongate with age and as the plant clumps up with many heads.