hi start feeding with the 10 10 10 in very small amount, your plant is at the 3rd week mark, she is still tiny due to her roots have not hit bottom of the pot. at the 3rd week in veg you start a light feed, this is how you get growth going as starting in the 3rd week your plants cell structure changes from seedling to young plant.
so remember that you feed lightly and move up the dose after a week of use.
you can use the 10 10 10 through to the start of flower. once you start flower then you want to change your nutrient to a booster with no nitrogen, nitro gen is the first number of the 10 10 10.
so in flower just for instance you would want to use something in the lines of 0-30-50,
i recommend beastie bloomz by foxfarm, but in the end it is your choice. last you can always pick up some all purpose 20 20 20 this you can use through the veg cycle as well, until flower. so the next time you grow start with the 20/20/20 you just get more in it and it is a bit stronger than 10 10 10
with the 10 10 10 or the 20 20 20 it is designed to feed at every other watering. when you do use it for every other watering you do not mix it that strong, so if the label says this much than you use atleast half that amount. when your feeding now, you use a 1/4 of the amount. you also may want to pick something up for the roots, like great white or extreme gardening mykos
i use the extreme gardening mykos as my plants have never been happier. with this you would mix a table spoon or two in your soil mix.
right now like i said above, your plant is still bottoming out, tap root hit bottom of pot, once this happen you will see growth pretty much over night.
remember not to over water and making your plants water logged. like the food, a little goes a long way. hope this helps