What are potential sources of low recovery in this acid-base extraction experiment?
I can only assume that you we following some recipe for the purification of the benzoic acid. Frankly if I were doing this I would have done it differently. 

Wikipedia shows that the solubility of benzoic acid is 1.7 g/L (0 °C) and 56.31 g/L (100 °C) in water. So I'd added benzoic acid to a test tube and put in a boiling water bath. I'd added just enough water to get the benzoic acid to dissolve and then let the liquid cool in air. When down to room temp, I'd put it into an ice bath. After 10 minutes in ice bath I'd pour off water. I'd wash with a few drops of ice cold water. I'd test for purity and if not good enough I'd repeat. 

0.34 g of crude benzoic acid should dissolve in about 6 ml of boiling water. 

Each water cycle should have an efficiency of close to (56.31 - 1.7)/56.31 = 97%