I know this is hard advice to follow, but if I were you I would not waste my mental energy on worrying about peritoneal mets when you have no idea whether you have them or not.
It's true that there are rarely any symptoms until much later in the advancement of the cancer spread regarding peritoneal involvement. My husband had them, and he had no symptoms of them until the last 6 months - then he had bloating, mild discomfort, and ascites. He certainly never had blood in his urine, however!
My husband was told from the get-go that it was likely he would have mets in the peritoneum since his colon tumor broke through the colon wall before he was diagnosed. The onc did not say it was 100% likely, but eventually they found evidence in the CTs. I think it took at least 16-18 months after his surgery before the oncologist stated they were there definitively. As someone else noted, they don't show up on CTs for a long time. My husband's CEA began to rise a bit around the time they saw the peritoneal mets. It is a tough place to see the cancer spread to. Sadly, chemo is not as effective on the peri mets as it is on liver/lung tumors.
Good luck! I know how hard it is not to obsess about things.