Can you please check my sentences? Thank you.

I'd rather you went to bed early tonight.
2) I'm used/was used to drinking a lot of water in the morning.
3) I'd rather go to the dentist today than tomorrow.
4) He asked me if I could leave him a message on his answerphone.
5) I wish I had studied harder for my exam.
6) Briefly outline the main features of the epic poem. Refer then to the seventh-century (?) epic poem "Beowulf" and to what it celebrates.
7) Who is Beowulf and how is he presented in his fight against the fire-breathing dragon? What actions do each of them perform to kill the other?

Which sentences/questions do you have doubts about?

Sure! Here are the corrections and suggestions for your sentences:

1) I'd rather you go to bed early tonight.
- "Went" should be changed to "go" to maintain the correct verb form.

2) I'm used to drinking a lot of water in the morning.
- "Was used to" is not incorrect, but using "I'm used to" sounds more natural.

3) I'd rather go to the dentist today than tomorrow.
- No corrections needed. The sentence is grammatically correct.

4) He asked me if I could leave him a message on his answering machine.
- "Answerphone" should be changed to "answering machine," which is a more commonly used term.

5) I wish I had studied harder for my exam.
- No corrections needed. The sentence is grammatically correct.

6) Briefly outline the main features of the epic poem. Then refer to the seventh-century epic poem "Beowulf" and its subject matter.
- Added "Then" to clarify the sequence of actions. "Subject matter" is a more appropriate term than "what it celebrates."

7) Who is Beowulf and how is he presented in his fight against the fire-breathing dragon? What actions do they perform to try and kill each other?
- Changed "each of them" to "they" to maintain consistency in the sentence. "Try and kill each other" is more accurate, as it highlights the attempted action rather than the successful killing.

Remember to proofread and double-check your work to ensure accuracy.