Need to see pictures, how long was it vegged for?
Yields all depend on the strain and you, If you have it all dialed in(temp, RH, Co2) and know your strain well ( a few grows using it) and are training it because 250watts doesn't have much light penetration.
lets say if you chopped and dried now you got 30grams, if you waited till it was done then i would say at the end you would probably be looking at 60g maybe 75 if you're lucky.
You should also note breeders descriptions on time are usually a week or two off and most of them dont count "flowering" till they start seeing pistil's(hairs) forming which is a week or so after you flip to 12/12. That time is also based on their ideal pheno of the strain so yours may take more or less time depending on how it leans towards indica/sativa. So dont go cutting your plant on day 60, wait till you see the p[FONT=arial, sans-serif]istil's turning brown/red and receding and the buds swelling up. You can also use a 60x-100x [/FONT]jewelers loupe/magnifying glass to check on the trichome's aiming for mostly cloudy.[h=1][/h]