Seems to be happening all too often in the NHS. This is exactly what happened to me. I assume you had negative margins?
So we both have the long waiting for years, sadly, hoping to get regular "undetectable" results. After the shock of my T3a I decided to reduce my, already limited, alcohol to zero (or as near as). Similar I consume red meat and UPFs infrequently - I never had much before, but now I'm even more observant. I've run for decades and that will be maintained for as long as I can. I'm 14 months post-op and have convinced myself, most days anyway!, that PCa is in my past - reality may decide a different outcome, but I'm doing what I can, without getting obsessive about it.
My surgeon said, he believed he'd removed all my prostate and adjacent infected cells, and the negative margins helped to confirm that. He then added that there was little difference at this point in outcomes between T2 and T3a as the surgeons' skills in removing the gland and nerves etc, are key in whether or not any risky tissue was left behind. I trust him, which helped me a lot post surgery as I came to terms with what lay ahead of me.
You're unlikely to be able to shut out the period just before each test, but hopefully, after each good result you'll go for weeks where it drops out of your head as you work through your plumbing ups and downs, and get on with life.
If you can keep adding to your profile as tests come and go, it will allow those whose histology have been upgraded to T3a, which does feel so much worse.
Fingers crossed ...