As long as designers want to dress me, photographers want to take my picture and companies think my face will help their products, then I won't go anywhere until they're done with me.
No matter what - rehearsed, under-rehearsed, over-rehearsed, doubts about rehearsing - the first gig is always the first gig, and you put on your little praying hat, batten down the hatch, and do what you do.