Don't worry, just give it time. Zucchini plants tend to do a flush of male flowers and then send up the female ones. If you are really concerned about not getting enough fruit, you could try hand-pollinating them. All you do is take a male flower and rub the pollen on a female flower. It's best to do this in the morning right after they bloom. Supposedly, this is when they are most receptive to pollen.
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