seeing as you only have one plant on the go, the best option would have been cloning it while it was still vegging, (allowing it to continue growing) and then sexing the clone, but it's too late.
you might be able to get it to veg again if you switch it back after you've determined the sex, but it may be too late.
remember, force-flowering and/or a wack light schedule can induce instability in a plant causing it to hermi.