Please back the light off to 24 inches above the canopy.
20 inches is just a little close. Your plant will thank you.
I don't understand your reasoning for a mix and match potting medium as you describe.
In the future if you want to grow in Coco Grow. It's best to grow in Coco.
Check out Coco for Cannabis it's a great place to learn about growing in Coco.
Cannabis grow guide: articles, tutorials, DIY projects & more! Dedicated to the science and practice of growing cannabis in coco perlite and other media.
www.cocoforcannabis.com
The same goes for growing in Living soil or a Peat Moss based potting medium
like Pro Mix..
These are all great mediums for growing, But each has it's little differences.
I don't think mixing them all together like you have done is going to gain you anything.
in fact It's hard to offer advice as each medium has it's quirks. It's best to pick a medium and go with it.
That being said. I'm sorry to sound so negative. But, I rather enjoy helping new guys get themselves sorted and
have a great grow experience.
From what I see, your plant looks to be in pretty nice shape. Don't worry about her size. Some plants just take there time.
They grow a root system first. Then they start growing above ground.
What are you feeding her?
Do you have an E.C pen.
A, P.H pen and PH Down solution?
Any chance you added a little bone meal, Gypsum or Dolomite lime? Anything?
Do you have
Cal-Mag on hand ?
When growing in a tent it's best to keep your plant short and bushy. Down out of the light.
This is where LST / Low Stress Training comes in.
Your plant is not quite there yet, but you should check these videos out
so when the time comes you are prepared.