Something like that would want to make me curl up in the fetal position, cry, then die. I could just figure your face when talking to your agent:
"Sure no problem!"
Then when you get of the phone you're like:
"Scheiße!"
Well, I had one huge advantage. Those were pre-Internet days, and I didn't know enough to be intimidated. I knew nothing about writing, about technique, or mood, tone, flow, pace, characterization, etc.
I wrote my first short story just a couple of months prior. It sold, and so did the next two, all three in first draft form. Again, I didn't even know you were supposed to write more than one draft.
All I knew abut writing came from all the short stories and novels I'd read. All I did was write the kind of stories I'd read and loved. So writing a novel in three weeks, just meant dividing the number of words I needed by the number of days I had to write the, I think it came to something like 3,500 word per day, or a bit more. I don't remember exactly.
But I had all day, everyday to write, so that didn't seem like very many words, especially since I still didn't know anything about technique, or multiple drafts, or anything else.
It turned that writing that many words per day on a typewriter meant I spent all day, every day writing, and even ate most meals at the typewriter. But I did it.
Sometimes I think new writers try to learn too much before just writing a novel. All the techniques and methods, the outlining or not outlining, the pace, mood, tone, pace, flow, etc., gets confusing and slows everything down.
If I had my way, I'd tell new writers to forget trying to learn any of this until well after they write a novel. Just sit down and tell a story like all the ones you've read and loved.