Certified GKH Gardening Expert
It can take some time to eradicate weeds. You may consider raking off the gravel and applying a weed barrier cloth, then putting the gravel back. Some people use flame weeders for stubborn weed problems in gravel. There are safety precautions and this may not be a solution for you, but you may want to try it. Make sure you follow all the "rules," and best of luck to you. Here's an article that will help: https://www.gardeningknowhow.com/plant-problems/weeds/what-is-flame-weeding-information-on-flame-weeding-in-gardens.htm
and another on general weed killing in gravel: https://www.gardeningknowhow.com/plant-problems/weeds/controlling-gravel-weeds.htm
I have had good success keeping weeds under control in my gravel by spraying a mixture of salt and white vinegar. There was no need for me to buy the "super strength" vinegar, I used the cheap gallon-sized vinegar available at the supermarket, mixed with about a cup of table salt in a garden pump sprayer. Squirt on weeds, they will be yellowed within hours. Best done in heat of day so they absorb the salt/vinegar. Must be careful not to spray it anywhere you want anything to grow, because it really does stop everything from growing!