Unfortunately, if you wanted to grow a crabapple specifically to pick its fruits rather than simply as an ornamental tree, it would have been better to buy one or two cordon trained varieties on a semi dwarfing rootstock such as M26, such as those listed here https://www.pomonafruits.co.uk/fruit-nut-trees/cordon-columnar-fruit-trees/cordon-crab-apple-trees-malus. If you have the space, you might want to consider getting some; there are a few weeping forms of crabapple too, as well some naturally columnar varieties, though size of fruits might be an important factor to consider when looking at alternatives.
No matter how you try to prevent your tree from developing apical domination at this stage, I'm afraid it will always try to restore that for the next couple of years; its also likely not on dwarfing rootstock, so trying to keep it low and relatively small for ease of fruit picking may not be very successful. As the tree matures, it stops trying to shoot straight up; the crown tends to spread out sideways, with branches tending to droop down a bit lower - ultimate height and spread for this variety is around 5m x 3m. Recommended pruning time for crabapple trees is late winter, just before growth begins, and they fall into Prune Group 1 - light pruning only. In reality, you can prune lightly at other times without the tree coming to harm.