Breeding platties is almost enevitable, a few females to one male and you gonna get fry, nothing surer than that. What is the pH of your water. Platties thrive in water that is slightly alkaline pH 7.3 - 7.5 and a temperature of 25'C.
If all else fails try a different male.
But be sure you can handle (have space for) a large amount of these little beauties.
Regards
BigC