It's not you. The box is vastly too big, IMO. Filled with regular potting soil it will become a bog in short order. Azaleas are not bog plants...
Too much soil is as bad as too little. The soil in the box doesn't drain and there is A LOT of it. Bagged potting soil is made to retain water, not drain. Soggy soil inhibits root growth. It doesn't promote it.
Box should be at least half as small and simple bonsai soil used...
. Now it needs some to time to just grow and be adored. (Oops, that's what a kitten expects. )