Without a diary or more information, any reply can only be general in nature.
If you are growing an auto flowering plant, this is normal and a "trap" for those new to growing autos. Giving this plant any type of nutrient or supplement will not cause it to go back into vegetative growth, as once flowering has begun, it will not stop or change in any way due to nutrition.
If this is a photoperiod plant, the only reason it would be flowering now, is if you are giving it a 12/12 light schedule. Going to 18/6 (light/dark) will cause it to continue with vegetative growth. You can then go to 12/12 once you are happy with its size.
I suspect this may be an auto, and unfortunately, now that flowering has started, your plant will not grow a great deal more and will be concentrating on flower production, even though it is still quite small, as flowering in autos is regulated by age and not by size or by day length/light cycle.
Your plant does also seem a bit pale, more nitrogen would have helped her to gain some size, but as it is now, the opportunity for any further dramatic increase in size, has well and truly passed. With autos, it is important to get them to a maximum size in the first four weeks, before flowering commences "automatically" and much further growth in stature/size will not happen any more, now that this plant has started flowering.
I would recommend growing photoperiod plants, they are more easily grown to a suitable size before flowering is initiated manually and by you, by changing the lighting schedule. This way you will have decent sized plants with a much better harvest potential, all while having (possibly) reduced electricity consumption.
Hope this helps,.........
Organoman.