Delay spray not working

Hey guys. So I’ve been using stud 500 one of the many delay sprays in the market to last longer. So 30 minutes before the action I use 3 sprays. One on the top shaft, one below the shaft and one on the head. And then I rub it properly over those areas and keep it for 30 minutes. The first 2-3 times it worked well, though it was a bit to get hard but I was able to delay ejaculation. But for the past two attempts, the spray just stopped working. Last night my girl was riding me and I came in 15 seconds despite using the spray as I described above. What exactly am I doing wrong that the delay spray isn’t working for me. I really fucking want it to work so that I can give my girl body trembling orgasms. Please help!