Once a plant bolts and starts to go to seed there is nothing you can do.* Very hot weather will do that to many veggies.* I get your hardiness zone as 8.* You can check it here.
This planting calendar on the second page is for Missouri which has zones 4 through 7.* If you are in zone 8 use the later dates for planting.* It says to plant broccoli from 7/25 to 7/30.
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.