is it too late to stop flowering?

so this is my first time growing a plant and i accidently started rightaway with a 12-12 lighting setup.... it is now 4 weeks old...seing as its been in "budding" mode since the beggining is it too late to switch to 18-6 to allow it to grow larger befor it budds?

not if the plant is no0t showing sex yet....just put it on 18/6 if you want to keep vegging...or you can keep going 12/12 and you will get bud...just maybe not very much

if i leave it in budding mode how much taller will my plant grow?

Could double, maybe triple in mass/height.

Its never to late really. It would go into shock and all. There are some threads on revegging maybe do a search.

If you have had 12/12 from day one then your plant will probably not still double or tripple in hight but stay around what it is now and start to flower. You can always revert back to veg no matter how long you have been flowering, itll only take longer to start growing again the farther into flowering it has gone.
If you dont even have any signs of sex yet, which i find strange after 4 weeks, then you wont have much of a problem going back to veg.