Worried something missed during gastroscopy

Hi there. I had a gastroscopy done recently after suffering from abdominal discomfort and bloating and a single erosion to the antrum was found. A biopsy was taken to test for H. Pylori but this was negative. I have now been returned back to the care of my GP. I’m just worrying that the biopsy wasn’t sent away for further investigation. Can an endoscopist tell just by looking at a lesion that it’s not cancerous? I have since been put on Omeprazole and I take Gaviscon but they aren’t giving me any relief.