I'm not overly savvy on micronutrient deficiencies but your plant likely has one. At this early stage of its growth fertilizers, especially inorganic ones, are a dicey game so I would suggest something light on the roots and loaded with vitamins and micronutrients like superthrive. Add a drop of superthrive to every litre of a sprout's water and, if it's getting enough light and the proper amount of water, you'll notice more healthy growth. But it is still young, so if you have no access to micronutrient supplements, just give it some time to kick back and get through its awkward stage and you may see some improvement on its own. Cannabis has a happy habit of making do with what it has.