Hello rabbit bro!
I also had slow growth in my first attempt. This was caused of over watering and very low air humidity like 30% only. I was suggested to add H2O2 to my water. I don't really remember the amount. But it was very very little. like 1 ml per 10l of water or something. Maybe just search for the correct dose. I've heard people call it liquid oxygen. it help roots to become normal again and start to develop new root growth. After one time adding H2O2 things went smoothly. maybe you should try this. Also - don't over water ever. Better is to let the soil dry out than all the time being wet. Wen you let it dry out, it opens all the pores for sucking in the tiny amount of water that is left in this dry soil and there comes more oxygen in the roots as well. So by next watering it will take every food that you give them. When you over water. Plant feels like in swamp. Roots close all the pores and they don't take any oxygen and don't develop. Plant doesn't need bigger roots, because it doesn't have to grow them for finding water in bigger area. This is how I understand the irrigation of plant.
So my suggestion is to add H2O2 by next watering and then let the soil dry out. Just keep on watching that plant doesn't start to yellow by having no water. and then you can smoothly start to go back to your feeding plans. I am not really specialist of nutes, because I think that good soil has enough food inside already. I was transplanting my plant three times during veg. So every time it got fresh soil with all the food inside. In later stages when you feel that plant has taken everything from soil you can add some nutes. I know many people will disagree with me. But this method makes things easier. Plant knows what it needs and takes it from soil itself. When you feed it from early stages it can cause some locks, defs and everything. I haven't had such problems. I am only in half way of my second grow of course and can't tell you all the truth, but I tell you how it works for me.
For raising humidity I bought little air humidifier but it looks like even it doesn't fit in your cab. Or maybe humidity isn't issue for you.