Don't worry to much about the bulking up of the buds part.
As long as you keep her healthy and free from deficiencies she'll take care of the bulking up part on her own
Most of the weight is gained as the flowers mature and swell, and 6 weeks flowering is still early days, especially for a plant from seed.
I've been told patience is a very useful tool to have when gardening
Best way to see when she's finished is to get a 60x magnifier and check out the trichome heads.
Trichomes
Heres a picture of one of the flowers from the lower internodes on my critical mass. Took it with a cheapo usb-microscope I got of ebay.