theres a couple ways to keep them small first keep the lights as close as you can with out burning, you can also get this stuff called Bush Monster it makes your plants bushy and short.. and then theres topping your plant witch is pinching off the very new growth off the top of your plant.. AND one more way is Low Stress Training (LST)
GROWFAQ read all 4 also check out this thread
How do I keep my plant small? also I would do a little more research about putting your clones straight into flowering, I heard thats not smart you will and up with weak buds.