Ok most people are just coming off as insulting by stating facts but not elaborating further. Unfortunately these guys are correct, the plants are a bit small for 3 weeks. But don't get me wrong, overall they look really healthy! It just seems that you should give your girls a little bit more space, try planting them in a larger container if you can. Those look like they're one gallon pots and they're likely getting root bound and can be transplanted into 3-10 gallon plants depending on the size of your lights. I think that if you transplant your girls into larger containers you'll notice a big difference in size fast, the plants will literally explode in growth if you get a larger pot. If you can afford it, look into getting mycorrhizae.
http://www.amazon.com/Xtreme-Gardening-4402-Mykos-2-2-Pound/dp/B003STB5N6/ref=sr_1_1?ie=UTF8&qid=1391229209&sr=8-1&keywords=mycorrhizae
What you do is dig the hole for the transplant, but before making the transplant you fill the hole with the mykos. It's pretty much beneficial fungi that helps stimulate root growth as well as more efficient usage of nutrients. These micro-organisms are able to break down the nutrients into your soil, they literally eat your nutes in the soil and poop it back out in a way that is much much easier for the plants to obtain through their roots. So not only does this product help tremendously with root growth, but makes your feeding more efficient as well.
The reason I bring this part up is because if the larger pot size doesn't fix your problem, your plant might not be getting enough nutes. Before pumping it with more nutes, try the mykos for a week and note the results. If the plant still seems like it is sluggish in growth, just give it a tad bit more nutes than normal. Always take it slow with upping the dose of your nutes!
Again, these guys are 100% correct about the plants being too small for 3 weeks. But, the plants are also looking quite healthy. I bet if you look at the bottom of the pots they'll be rootbound if not close to it. Transplant to a larger pot and watch your girls thank you for it! And of course, keep posting on forums like these with any questions you have along the way. People like you who are willing to ask questions and admit they don't know everything will usually yield more than those too stubborn to ask for help. You asking this question will help your plants out greatly if you grab some larger pots. Keep asking questions and best of luck with your grow man! Just don't overthink it, it's just a plant and will do what it does best. All you need to do is provide it with what it needs. You've made it this far so I'm sure you'll get a pretty good harvest after all is said and done. More importantly, you'll have the experience to use for your next grow!