it's the wrong time of the year (at least in the northern hemisphere) to sow D. gigantea seeds. And they do not need a cold but a "hot stratification".
You surely know that they are tuberous. I treat them like most of my tuberous drosera seeds: I sow D. gigantea in summer (July) and put them to a sunny hot place.
After sowing I allow the pot to dry out completely. In September I start to water again and to keep them wet. With colder temperatures and shorter days you will get germination approx. in November/December. In the best case. And then you need some years patience to get them grown to adult plants.
I just took a photo with a pot of 2-year-old seedlings (sown in summer 2016). In the first year most of them stay in a rosetted stage, in the second year they start with an upright growth.