Welcome to the forums and thus the community, I feel honored to welcome such a handy person as yourself to our little community.
First off amazing job on the home built box, very resourceful I know that took a fair share of labour hours planning and thinking and possibly some unpleasant words but dang that’s a nice little grow box.
Should be great to start a first plant in maybe even finish bit ideally you will want something bigger, 2x2 is fine but 4ft is short… Maybe to short after your first grow but for now let’s make sure your as successful as you can be with what you have until you gain the knowledge and items you will need going forward.
My first question is going to be what lights exactly are in there? This information will be important
My second is are you monitoring your humidity?
Do you have a dehumidifier or humidifier on standby? Ps your humidity is going to want to be like 90% in there until the plant is about half the size you want it to be, then you’ll flip to flower.
My third is have you taken a LUX app on your phone and taken a reading at the top of your plant to see how much light intensity your getting currently? If not please do so.
What’s your light timer doing? 18/6 for photo periods but the first two weeks you can do 24/0 or 20/4 on/off.
Flip to 12/12 or 11/13 when your plants at 50-70% max height you can handle because it will stretch.
A suggestion for now would be to boost the humidity and if you have to dome the plant, humidity is almost more important than light right now not quite but close.
Find something clear and cut it in half if you must but dome it to trap the humidity.
Do you let your water sit out for 24hr prior to giving it? You should this removes chlorine and brings it to a better accepted room temp.
What type of medium? Soil? If so what type?
Soil less? If so what type & mix 70/30 coco/perlite?
Have you chose a nutrient line yet?
You don’t have a carbon filter so you’ll be okay with the stink from flower?
If not look into 4invh carbon filters you can attach it to the exhaust vent.
I’m guessing you should drop your light if possible, if not then you should make it adjustable, same with your CFL’s make them all adjustable on rachet hangers or rig something up yourself in your shop.