How to have the same amount of bacteria growth on each petri dish?

For a (high)school project (again…we changed it) we’re going to look at the anti-bacterial abilities of different spices. I will list our initial method below. But our teacher pointed out, that if you swap 7 times the amount of bacteria will differ each time. How can we make sure the amount of bacteria is the same in each petri dish? We thought about making it a dilution and applying the same amount of on each petri dish. Would that be an idea? Additionally, what else could be improved on?

1. Prepare the growth medium, which consists of agar mixed with herbs. Prepare:
   • 1 agar plate with parsley
   • 1 agar plate with chives
   • 1 agar plate with dill
   • 1 agar plate with shiso
   • 1 agar plate with ginger
   • 1 agar plate with wasabi
   • 1 blank control plate containing only agar without any herbs, to check for contamination.
2. After rinsing, swab the inside of one cheek thoroughly (approximately 20 times) with a rotating motion using a sterile swab.
3. Repeat this process for the other cheek, using a new sterile swab. Swab the entire inner surface about 20 times as well.
4. After swabbing both cheeks, wipe the swabs onto the agar surface of the Petri dishes. Do this for  according to the scheme provided below.
5. Incubate the Petri dishes for 24–48 hours to allow bacterial colonies to grow.
6. After incubation, count and record the number of bacterial colonies that have grown on each plate.