Spray the top of the soil as well with a good soaking. Or mix some neem meal into the top of the soil but not much as it's pretty high in nitrogen.
I've always knocked fungus gnats out just by spraying the top of the soil with neem. The sticky traps work for the adults but there will still be eggs and larvae in your soil.
Some even go as far as to do a soil drench with neem but there is debate on whether that will effect the taste of the cannabis.