Heh, to make it go back into the vegetative stage at this point would probably take longer than just growing another plant. If you don't think you're going to get enough bud on that plant to be worth flowering it to completion (it's probably not going to get much bigger than it is now, after a month of flowering), and you have more seeds, kill it and start over. Sorry to say that; I know it sucks.

Pot size is crucial (because of the root mass issue). What I usually do is start a seed in those little marshmallow-shaped sponge things, let it sprout and get a few roots going, then transplant to a 1/2-gallon pot. I let it grow a couple of weeks and then transplant to a 4-gallon pot. Then I let it go a couple more weeks or so to let the roots spread around inside the bigger pot (and the plant above ground to get bigger too, of course). And then into flowering it goes.

If it's not a pot size issue, then I dunno, could be a genetically inferior specimen you have there. Just like there are flimsy, sickly people, there are also flimsy, sickly plants. Maybe that's what you have.