What hours should I be working on Salary?

So I recently started a job that pays salary.

In the contract I signed it says that I get paid for 40 hours a week with no over time.

My question is my boss wants me to work, a lot.

Weekend, night, early mornings.

I’ve never had a job that is salary before. Is this normal? Should I HAVE to work like that?

I mean it doesn’t matter if I work 100 hours a week I still only get paid for 40.

Thanks!