Please help! What size pot containers are good? Is 3 gallons ok for 15-21" plants

I just started flowering yesterday. My plants are a average of 15" the tallest one is 21" is the 3 gallon pots they are currently in going to be fine?, or do I need to put them in bigger pots? If it doesnt make much of a difference id love to just leave them alone so as not to stress them out. The strains are 1. Cheese. 2 sour diesel and 3 skunk #1 im starting to think about this because the 21" skunk leaves are curled inward and ive tried to fix it but nothing is working besides that the plant is healthy and all the other plants are really healthy only thing i could come up with is maybe the leaves are curling due to the 3 gallon pot being to small. Thanks everyone.

I finished at just over 4' at 8oz last year in a 3gal.

Wow 1st time. Was that 8oz one plant? What wattage are you using? Im using a 1000 watt hortilux red eye hps on those 6 plants i mentioned above plus i have a few autoflower mig 29's finishing up in there the latest one should be ready to pull in 3 weeks. I'm trying to keep my expectations low so as not to be disapointed if I don't get a good yield. I'm expecting or lol hoping for atleast 6ounces, one for each plant but man if I could pull double that it would be great thanks for the reply it's very encouraging.

8oz, one plant. Lost 2oz to mould. How many watts is the sun?