I have been through this. If you are constipated this could have caused the trace blood if you have piles inside.
Low estrogen can cause constipation, it was one of the things that stood out for me.
I had the 2WW colonoscopy and it came back with polyps. I didnt have visible blood either. Polyps are very common, 1 in 4 people in middle age onwards have them. Some have potential to develop into something (over a long period of time), others are just overgrowth of normap bowel tissue. Both types are very easy to remove. I had mine removed during the colonoscopy and a follow up colonoscopy the next year and all was fine.
There are so many things it can be other than something sinister, please be assured of that.
Are you drinking enough water and eating enough fibre?
Ask as many questions as you want, there are loads of women on here who have been through this and come out the other side! Very very few (I think only 2 from all my searching on here) had anything really wrong. Most were polyps, diverticulitis, inflammatory bowel etc. Believe me, I searched and searched when my test came back elevated!!
Also with the scan and bloods, pretty sure they'd have done CA125 test and therefore ruled out anything ovarian, so don't let your mind go down that route.