What to do with a rootbound auto in flower?

Need some advice, pretty sure this girl is rootbound, she's in a 3 gallon fabric, canna terra pro soil, the pot never seems to get heavy after water feeding, she's always a little droopy and sad looking, pale green colour she's getting canna flores and a little cal mag due to a mag deficiency, probably 3 1/2 weeks into flower, this strain is a long flowering auto the last o e I did went 90 plus days, is it to risky to up pot? Any other options out there? The last pic is of the same strain at 90 plus days

If it's not getting heavy, is it possible your soil has gone hydrophobic and isn't soaking up the water? Maybe try letting it soak up the water from the bottom until it gets saturated?

I'll give it a try, thanks