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It sounds like you're doing

It sounds like you're doing all the right things, Susan. 

One suggestion is to maybe let nature take its course. The plants produce both male and female flowers, usually enough for pollination.

One question: are you pollinating in the morning? At that time, high humidity helps to activate the pollen.

Then again, sometimes plants produce all male or all female flowers. The sex can be influenced by temperature, day length, maturity and hormones.

One other thought: back off the watering for a bit. While zucchs like moisture, they also appreciate a brief dry period between soaks.

Hope something happens soon...