As a newbie myself with only a few hours supervised under my belt , I can honestly say it's probably one of the best decisions I've made is to get into the left hand seat of a light aircraft and take control of it , even if it is only a few minutes at a time for the moment. The one thing you can't have imo is doubts of any kind ,as once you're in the air you must be confident enough and focused enough to concentrate on the task in hand, but this is only your first lesson so the instructor won't force you to take the controls or expect you to do anything you don't feel up to.
As for safety ... well if you are worried about that then why drive a car .. or walk across roads ? There's a risk in every action we take in life all we can do is minimise that risk to the absolute minimum and that's why to obtain your wings you have to undertake all those exams , hours of flights and pass a medical. If It is unduly worrying you though, maybe you should resolve any issues you have with flying before committing ?