JLS1
A TURBT, like all tests has limitations.
IF the doctor see a suspicious area, s/he can take a sample to be examined.
IF the doctor does not visually identify anything suspicious, yet has cause (such as a positive cytology) to suspect cancer, s/he may take random sample biopsies to be examined by the pathologist.
blue light inspection of the bladder MAY be helpful to identify cancer in the bladder that cannot be seen under normal white light. This test also has limitations.
If nothing is found in the bladder, yet cytology continues to indicate suspicion of cancer, it can become reasonable to consider the possibility of upper urinary tract cancer - that is, cancer in the ureters or renal pelvis. There are a number of tests to evaluate the upper tract, when it is warranted.
Talk to your doc/care team - Ask what else they can do to find the source of the "cancer in your urine" that you mentioned, and what is the appropriate time to consider further investigation.
Best
Jack