Genetics can cause some plants to be more compact and short. Also the amount of light it is getting in relation to feed will also play a role on how fast it can grow. Plus the lights spectrum. far red and red cause more stretching where as blue caused more compacted growth.
Topping and FIM'ing will have negative effects on the plants height and take it some time to recover. It looks a bit small for 8 week veg buy you have also used HST on 3 of the weeks in its life, so its not to bad. I did a diary of plants that had a lot of HST and they are in similar size range. Best to let it grow out some more and keep up the feeds as you switch to flower.
growdiaries.com/diaries/129773-grow-journal-by-m0use/week/725147
Best Of Luck!