How do marijuana plants form buds?

How do marijuana buds coz I'm growing some purple kush but I got the seeds cheap because they're mixed male and female they're also the old stock seeds which they didn't sell so instead of paying like 30$ for 3 seeds I payed 10$ for 300 mixed seeds with guaranteed females and guaranteed good seeds...ive been growing mine for 3 months now however & they look really tall, showing signs of being female but I was told that they should be bushy right now with loads of fan leaves however I've got 6 branches with fan leaves... when It starts producing buds are they only gonna grow where there's twigs of fan leaves or will new branches form all the way down the main stalk?? Thanks