The fact that you are having these doubts, Andy, suggests that all is well and you should carry on singing. The singers I find most difficult to tolerate are people who seem quite unconcerned about the quality of the sound they are emitting, the sense of the words, the charm of the melody, or indeed the point of singing the song at all. If you are aware that all these things matter, you're probably doing fine. And remember, it's not about you, it's about the song - this may help you to be less anxious about your performance.

Marje