Banana flowers are a lady's last ditch effort to procreate, and usually results from some kind of stress (although some strains are prone) so look for any issues that might be causing this: less light than 12/12, too much light/over 12/12, high heat, large temp drops between lights on and off, nute/ph issues. That said, save your little bananas, dry them, and store them in a baggie, and on another plant of the same strain, late in flowering, gently brush pollen on lower buds. You will then get feminized seeds, i.e., seeds that will produce female plants. I like to do this every so often so I've got a bank of seeds from a strain I like, and true to claims, feminized seeds produce more than 90-95% female plants.