It's easy to spend an hour or more scrolling through social media at bedtime (I know I've done it myself on occasion). Do yourself a favour and use that time to sleep instead - teenagers need between 8 to 10 hours a night!
I used to be scared of asking questions at school in case I looked stupid, but then I would end up looking stupid because I hadn't asked the question. The worst case scenario is that your question is a silly one and someone might giggle or the teacher might grumble. On the other hand, if you ask a question, it shows that you are interested, listening and thinking about the topic. It is also better to ask a question and check that you only have to do questions 3 and 4 for homework, rather than staying silent and doing questions 1-10 because you weren't sure. 99% of the time it's better to ask the question.
This is a good principal for all areas of life, whether you're tackling homework, chores or your to do list. If you put off the hard things you will most likely run out of motivation and possibly time. If you do the hard things first, you will be more likely to have the motivation to keep going through the easier tasks too. Plus you will have the satisfaction of crossing them off your list, rather than the nagging dread that they still need to be done.