Not necessarily wrong, but it sounds more natural to say:
2. If you have submitted your paper to the professor, you can
have some days off.
And I think your verb tenses are confused here:
3. You don't think I'm good at singing. Even if I had sung you a serenade, you wouldn't have paid attention to me.
Or:
3. You don't think I'm good at singing. Even if I sang you a serenade, you wouldn't pay attention to me.
Or:
3. You don't think I'm good at singing. Even if I sing you a serenade, you won't pay me attention.
Do you mean to say that the person is now a liar, but you didn't think that would happen?
4. I didn't think you would become a liar. If I had listened to my friends' advice, I would have broken up with you.
And I don't think you typically need the "now", it's implied by the context:
5.If it's raining now, we ought to drive back to the movie theater.
