My Plants Stop Growing Vertically

I Am A 100% Newb At Growing, And I'm Only growing One, just for experimentation you know? I'm Learning slowly, I've got, a Big 12' x 12' Pot for my plant, I've got mirical grow "all purpose" and I'm using 3 compressed Flouresent light bulb, one is 40 watt's the other two are 15 Watt's Daylight, i've only just turned 17, dont got a job, so i cant really afford these 400$ Metal Halid Light bulb's and shit, i'm on tight budget, but my plant was growing really quick really healthy and strong, i have it in a 5 foot tall cylender of cardboard and the inside is laced of tinfoil i have my three lights in it with a whole for my fan for ventalation, we'l.. there really really slowed down growing vertilcally, i just started growing like 2 weeks ago, can somone give me a tip?

tin foil will not reflect light as much as it will heat, causing some burning, so take that out and get some mylar, or get just some white paper and line it in there. on the vertical growth not 100% sure, as long as the plant looks green and healthy and the roots aren't filling the pot / have no more room to expand.... you should be ok.. sure other people can help too. good luck man

thanks dude

Most good hardware stores (OSH, Lowes etc.) sell an aluminized foam core sheet, 4 feet wide for about $2.50/lf. The stuff is pretty stable, much like cardboard, and if you get 6 or 8 feet you can enlarge it as your plant gets bigger.