Bigger light, bigger buds.
It is that simple.
If you want yield, forget autos, photoperiod plants are the ONLY way to go.
Plus they have 40 odd years of development behind them, almost guaranteeing better results, plus YOU get to control when they flower.
Giving humic/fulvic/amino acids, or all three will boost your buds, as will adding a mycorrhizae to your soil mix before you plant. Mykos made by Xtreme Gardening is AWESOME and while a bit pricy, it is worth every cent. Besides, you don't need to add much, so one packet goes a long way. eBay have it if you have trouble finding it.
In future, with this light, I would suggest growing only one photoperiod plant and using a 20-40 litre pot. Combined with some LST or SCROG, you will get much, much more than from any silly autoflowering plant. Try Sweet Seeds, all their strains are superb, Sweet Zenzation is fast flowering and a knockout with dense, resin dripping buds, as are most of their strains, you really can't go wrong with anything with the Sweet Seeds label. I have been growing for 35+ years and have tried many seedbanks and these days, Sweet Seeds are my "go to" breeder. I have tried nearly every strain they have and am yet to come across a dud. They must be the most under rated breeder out there, yet all their strains are super simple to grow, potent and if grown right, huge!
Hope this helps,...............
Organoman,
(and sworn enemy of autoflowers!)