The pot is way too small and you topped it, as said it is stunted. Get a 2 - 3 gallon pot. Germinate a seed on a paper towel. Fill the pot leaving an inch gap to the top. Soak the pot in plain water. Plant the seedling. Leave it in daylight for a couple of days, until you see green leaves. Then stick it under a light 24/7. When it grows up 3 nodes, bend it over gently and use a tent peg to hold it down. Then keep moving the peg every time it grows up a node. The idea is to keep it flat so the side shoots become tops. You may need more pegs as the side shoots grow.
Instead of using coco why not try some simple store bought compost, the type of stuff you'd use for tomatoes. You can use plain water for a couple of weeks and then slowly introduce some tomato feed, start at 50% and work you way up to full strength over a couple of weeks with a touch of epsom salts every other feed. Feed/water weekly or when the pot becomes light when you lift it.
I am on my 3rd run with Autos and my last batch was done using the method above and it has produced some of the sweetest weed I have ever smoked. Never top or repot an Auto and keep it super simple.
