Tunesmith is correct!! Also consider when you did your trial run, was it using the EXACT same equipment the studio will have??? All the more reason, as a vocalist, to focus on EMOTION, and PITCH; i.e. performance. You just go in there and sing your heart out. Let your production team deal with everything else. When you are done, if you are dissatisfied, have an honest conversation with yourself as to whether it was the performance or the production/engineering team. I have seen both sides many times.
Hope that helps.