What can I do to improve my resume?

It depends on what your resume looks like now and why you're worried about not getting in. You can look at the chancing breakdown on CollegeVine to see where your biggest areas of improvement could be.

1. If you are worried about your grades -- you should focus on studying for your classes. If there are certain classes that are challenging you, try talking with your teacher to figure out what you can do to understand the material better. If you know what you're struggling with, and why you're struggling with it, you can then better prepare yourself.

2. If you are worried about your test scores -- not sure if you've taken the ACT or SAT (or plan to take them) but you could always build a study plan to get your scores up if you're able to take them again (sometimes this is hard financially, but you could ask your school counselor for a fee waiver to reduce the cost). Pick one of the test, figure out which section(s) of the test you struggle most with (by taking a practice test) and then give those sections extra attention when you're studying.

3. If you are worried about your course difficulty -- within reason, make sure you're challenging yourself academically in high school. Take courses that are challenging but that you can handle. Colleges like to see that you've challenged yourself. OK grades in hard classes are usually better than GREAT grades in easy classes. But, make sure you know yourself and what you can handle. It's not worth driving yourself crazy and losing sleep by taking so many hard classes. Personal care and health are SO important.

4. If you are worried about your extracurriculars -- make sure you're doing ECs (clubs, jobs, hobbies, volunteering, sports, ...) that you are interested in. If there are opportunities for you to take more of a leadership position, then you should definitely consider that. If there isn't a club at your school that you're interested in, but you have an idea for a new one, try starting your own club! Don't add activities just for the sake of adding them. Add them with a purpose. You're more likely to do well and enjoy your activity if you have a genuine interest in it! Taking care of family members also counts as an activity that you can tell colleges about if that is something that you do!

Would you mind telling us a bit about what you already do and what major you are applying for? That would help us give more specific advice. Also, what high school year are you?

if you still have years then i recommend you do some extracurricular activities and just keep studying. that's all i recommend.