Welcome to somewhere you don't want to be!! But all of us have "been there, done that" so we know what you are facing and even a bit of how you feel.
First, to try to answer a few of your questions. The most common form of bladder cancer, transitional cell uretheal carcinoma, often presents as a little mushroom or tree-like structure growing out from the bladder lining. The odds are pretty good that something like this is malignant. Your urologist has had a LOT of experience looking at these critters!! Of course, he could be wrong. Only the results of the TURB will tell the true story....is it cancer and what grade/stage (how fast it might grow and how far has it gone so far.)
CT scans are one way of finding abnormalities, but as you have discovered they are not omnipotent. Neither are urine cytology tests or the urologist's eyes. The only way to know for sure what is there to to look at it directly, remove it, and send it to the pathology lab for analysis.
IF you should have bladder cancer, it is very likely that it was found early. Many of us here on the Forum have had this diagnosis and have been doing fine. I was diagnosed almost 11 years ago (high grade, non-invasive) and following treatment have had no recurrences or problems. You can do this too!!
Sara Anne