Thank you everyone, and to Confiteor Deo, Don Ruggero and phil in particular as those were the specific situations I had in mind. To me, concerts and choir rehearsal (much less singing practice from the Holy Father!) don’t compare to a random and unsolicited “performance” by a passing visitor in a church. I (very erroneously) believed it might be unwise, rude, uncharitable, etc. and therefore at least venially sinful to use a whole church for oneself…
Anyway, I am grateful to all those who have helped me to see how ridiculous my concern was - and I mean that! From an outside perspective, I understand how ridiculous scrupulosity seems. And it is ridiculous most of the time, there’s no denying that. This is another false concern obliterated and off my mind (phew!).
To all those who advised getting a spiritual director: please consider that many Catholics, especially like myself, are more eager for a spiritual director than you can imagine. I know that you’re well-meaning, but it’s not as if spiritual directors grow like weeds! God willing, I will have a spiritual director someday; it’s simply not the case for now.