I think it's a great you want to prove him wrong, however, if you truly find you don't understand the concepts enough, even with assistance, don't be afraid to drop the course. I'm not encouraging you to drop, rather I think it's best for you to keep all possibilities open. If the professor was for physics, I can understand his view because you posted you didn't read the chapters, which is problematic in the eyes of most professors as it shows you may not be committed. If he wasn't the physics prof, then he has lost sight of part of his job: helping students.

If you want extended time to complete coursework, generally you need to talk to the administration simply because the professors don't have the necessary authority.