gopher hit the nail on the head. I've grown a few crops of autoflowering and they will flower even if they are small.
From the description you have given it sounds like what my autoflowering plants are like at four weeks. I don't really keep track of how many weeks in my plants are (bad habit I know) but they don't seem to get the really vigorous growth until about half way through. Also don't be surprised if some of them just stay small.
I've got several autoflowering plants going right now and there is about a foot difference between the tallest and shortest plant.
My plants at about four weeks in (age is an estimate: it might have been more like 3 weeks but you get the idea right? Also sorry about the picture quality, crappy camera and I was showing off my new HID light not the plants)
My plants today (19 days latter)
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