You have about 8 sq. ft of floor space, enough for a few medium sized plants or maybe 5 smaller ones. As the others noted the plants can easily double in size by mid-way through flowering, and then they should stop stretching. Also, bigger plants are not always better unless you plan to incorporate sufficient side-lighting. You may notice when flowering larger plants that while the main cola and upper buds fill in and dense up well, lower buds end up much smaller and fluffier and the absolute lowest branches end up sickly, ultimately dying off or removed by the grower.
Also, container size does matter as a vigorous, healthy root system will translate into yields. You say your plants are in 1 gallon pots and that's fine for vegging but you'll want to transplant a week or so before you force flowering. You'll want to use something like a 3 or 5 gallon container, at least a gallon per foot of plant. If you expect your plants will finish at 3 feet then 3 gallons is good, otherwise use something larger.
