The biggest factor affecting yield is your lighting. For those nice tight buds, you are going to need quite a bit more light. A 600W is barely adequate for 16 sq ft and more would be better--either a single 1000W or 2 600W.
Genetics are also very important. Once in a great while you can get something good from bagseed, but generally the results are less than stellar. I encourage you to check out the seeds that are available now and pick something that sounds like something you would love. There is an advantage to knowing what you are growing--you will know the basic plant structure, you will know the type of high, you will know the flowering period, and lots more. Run your choice by the people here before you buy though to make sure the seed bank is reputable.
Do not add sugar to your grow--this does nothing good and can do bad things. Also CO2 unless it is monitored and regulated is a waste of money, time, energy, space. There is a lot more to CO2 enhancement than simply adding CO2 to your grow. Concentrating on the basics will give you the best crops. Leave the fancier stuff for later when you have some experience.
Good ventilation is almost as important as your lighting. You need good air exchange--out with the old and in with the new. This is generally accomplished with a centrifuge type fan that exhausts air out and passively brings air in. Ventilation is for more than cooling your space. Your plants need a continual supply of fresh air all the time the lights are on for proper photosynthesis.
However, you obviously did a lot of things right as you ended up with good bud, just not enough of it. This is a long process and a lot of new growers have to try several times. So, I would say that good genetics, more light, and making sure your ventilation is good will result in a lot better crop for you the next time around. Proper drying and curing will give you that good tasting bud.