Live performances are very dynamic in nature. There are so many variables. When we practice in the comfort of our own home , we are in a perfect scenario that barely ever presents any variables. Messing up a few notes or mixing up  lyrics is not that big a deal. It can happen to the best of us.  

There is a way to, however , minimize it and that is “PREPARATION”. If you are a well prepared singer, even if you messed up a few notes chances are you probably didn’t go off key. Adjusting, tweaking and modifying are all accepted in a live performance scenario. Preparation involves not only rehearsal of what you are singing but of various worst case scenarios. When you are on stage you should be so well rehearsed that you get on auto pilot where lyrics and melody is concerned and you are able to handle anything untoward or distracting easily.

It is also very important to learn that even if mistakes happen in a live situation, it should not be visible to the audience. You can privately just modify, adjust, smile and move on.