Just because you might be a first-time novelist, it doesn’t mean you’re not the authority over your work. No agent, publisher, or film producer knows more about the inner workings of your story than you.
They may have notes, and they may have some great ideas. None of those notes will help, however, if you abdicate authority over your work. Never agree to a note simply because you think it will improve the odds of selling your first novel.
The moment the first-time novelist abdicates authority over his novel is the moment he loses connection to something ineffable, something that is often difficult, and sometimes impossible to recover from.
When it comes to owning our work, there is no difference between being a first-time novelist and a seasoned veteran. Unless we’re anchored to what we’re attempting to express and are willing to hold onto that, we are just hacks.