All the FIT test is testing for is whether there is blood in your stool. Given that you saw a lot of blood, the test isn't telling you anything you didn't know. A high reading doesn't mean anything about cancer. It just means there's a good bit of blood there and you already knew that.

A number of things can cause that - diverticulitis, Crohn's, ulcerative colitis...

I had a number of symptoms of bowel cancer when I was 40. Different ones from you, but still and the consultant said that if my mother came in with those symptoms he'd be worried but at my age, it was possible but unlikely. In my case, it turned out to be hemorrhoids (probably combined with the effects of my thyroid medication and possibly the stress of the whole situation. The cause in your case is probably different, as the symptoms are very different, but I would say the odds are still against cancer.