Helpppppp! Quick Question!

Hey guys. i jsut started growing some chronic i got from my friend and its doing alright. its taken a month for it to grow about 4 inches. maybe because i left it growing on my window sill. but just recently i transplanted it into a bigger pot with a flourcent light over it for 12 hrs. it seems to be responding well but it just keeps getting talller not wider. how do i stop this? i attached some pictures but they are shitty. better ones coming soon. thanks a lot for your help!!!!!

me personally, i would get 2 or 3 cfl's and get them as close as possible, it seems like it didnt get enough light , but thats my opinion and im not a pro, (yet), i have a plant about 4 weeks in, its outside in a pot and its an easy 12" to 14" now.

Looks like it's streching for light, get it closer