What are some things I can improve last minute?

To answer your question, a GPA is something that is a long-term process, meaning it is an average of all the semesters of high school you have completed. Realistically speaking, it is hard to change your GPA exponentially in just one semester. My advice is that since you can't drastically change your GPA, I recommend owning it. Remember that GPA is just a number, and there are many other holistic factors that colleges want to know about. I am not saying that GPA is unimportant, but since it's your last semester, focus on creating compelling essays and showing colleges the best of you. Just a reminder that colleges are not looking for perfect GPAs; they want to see improvement. Put in your best effort in the last semester of high school. If you challenged yourself in your coursework, that is also an important factor. Some last-minute activities you can do are try to get online certifications for your areas of interest; there are many week-long online courses available out there for free. Most importantly, advocate for yourself! Show colleges why you want to attend their college. Don't give generic answers; do your research, and make sure to be specific about the professors you want to learn from. This can be overwhelming, but be confident; you've got this!