Can I trust that an endoscopy didn’t find cancer?

Hi all, I am 30F, 5foot 4 and roughly 12-13 stone 1 C-section 19 months ago, PCOS I have on and off suffered with heartburn my whole life But About 6 months ago it increased to every single day and it wasn’t relieved with Gaviscon I had an endoscopy which found ‘mild non erosive gastritis’ they did a biopsy for hpylori, which was negative. I was only off PPIs for 5 days so they also made me do a stool test after being off them for 2 weeks. This also came back negative. The treatment was then 6 weeks of daily omeprazole. This stopped the heartburn I was having but I’m still having a pain in my lower chest/upper stomach that hurts more after eating or drinking, I’m worried because, surely the omeprazole should be treating this? I’m due to stop taking my omeprazole in a few days as that’s the end of my treatment, but because it hasn’t helped I’m worried deep down the endoscopy could have missed cancer. Are they accurate? Would you want me to get another one done