If you’re constantly admonishing yourself about what you could have said and should have said, you’re going to live a pretty stressful and guilt-ridden life. These regrets will haunt you unless you stop making the mistake of not being assertive enough and not being “in the moment.” Stop editing yourself when you’re interacting (live or remote, but I’m not counting social media which are a cesspool of bullies and the insecure).
Say it, do it. You can always apologize if needed. But you can’t compensate for something you should have said after the moment is long gone.