I agree man, looks a lil small. What is your light setup? do u have a fan or circulating air in there like mastersaofan said? what's your soil?
No fans ATM going to put some in tonight and yes it's a little small maybe because I just started using nutes
2 problems I see, not enough light and 99% sure your soil is compacting. First problem is an easy fix, second one not so much. My suggestion is to get a bag of perlite and mix it into whatever you've got left of that soil at 2 parts soil, one part perlite. I'd also add a lot of other things to the soil mix but that's up to you. Transplant into your final pot with the new soil, if you can ditch some of the old soil without hurting the rootball that's exactly what I'd do. 4-packs of 26w bulbs are pretty cheap, hardware store has them for $14. You can wire up an additional 100w for less than $20, it's safe and easy if you're interested. Could also just be genetic, but you still want to improve your soil and lighting nonetheless. Cheers and good luck!!