WHY PLANT DOESNT GROW

Amico il primo problema che noto immediatamente sembra il lterreno , troppo compatto magari le radici hanno qualche problemino , comunque la pianta tutto sommato non sta andando male ,dal 10 agosto ad ora le giornate stanno cominciando ad accorciarsi perciò mi sembrano ad un buon punto considerando le ore di luce :) spero ti sia stato d'aiuto

Small, but doesn't look like 'many problems.' Especially for a first grow? I'm further along in my first and mine were also on the small side. I've learned a lot this first time through and now have a list of 'what I'll do differently next time.' Dense soil + vermiculite, which holds water are probably not the right direction for a grow medium as you want something light and that releases water quickly and easily. Maybe perlite next time. I agree that neem isn't good for young plants (and not good to use unless you've got a serious pest problem anyway), but the rest might be a combination of the water, temperature and whatever light situation you have. Take a look at the journal I have up if you want to compare my 'veg week 2' to where you are now.

Your soil seems very wet, young plants find it really hard to handle overwatering. Larger plants will probably not care unless absolutely flooded. At this point you only need your soil to be moist (not wet!). I am not quite sure what soil you are using but it looks dense and compost based - young plants can have problems growing roots in 'standard' garden soil - nothing you can do about it now I am afraid, it can slow the growth down. If there is compost in your soil you should not feed your plant at all when it is this small! Only thing I would try is some root stimulator, but no other nutrients. The leaves seem ok, so it may as well be your plant taking a pause to develop roots. My plants stopped growing in week 3, then a week after they started growing like crazy.

Check the ph. The plant can not take in nutrients without the soil being at the correct ph