Danny, I'm so sorry you're going through this. I know you're panicking and I know that feeling well, because I panic over my health also. It's a really dark place to be. It's even worse when you have physical symptoms, as you do now... Your mind tries so hard to explain the discomfort and usually comes up with the worst possible thing.
That story you read about the girl with the misdiagnosis, that kind of thing is incredibly rare. The chances of you having cancer of any kind are so slim it's not even worth thinking about. Your symptoms and test results all scream IBS.
I'm not sure if this will help, but sometimes it helps me to take this kind of thinking and flip it around. Imagine that the .000001% chance you're worrying about is instead something really good... Like imagine you just bought a lottery ticket and have a .000001% chance of winning a billion dollars. Would you be as certain about winning the lottery as you are that you have cancer? Not very likely, right? Your mind has a way of warping your perception and magnifying the thing you fear, so it seems like a much bigger threat than it is. And the physical discomfort you're feeling only makes it worse, because it gives you something real and tangible to link that awful fear to.
But what you're feeling is IBS. It's not cancer. Your biggest problem right now is that fear is getting to you and it's lying to you and making you miserable. You're a lot better off than you think. Truly!