Highschool Junior interested in becoming a nurse

Have you considered getting trained as a patient care tech and getting a job in a hospital? Depending on where you are, some hospitals will pay for you to go to school and employ you upon graduation.

Considering how difficult it is for new RN grads to get jobs you might want to look into this route.

See if your local hospitals offer career fairs or summer intetnships for high school students.

Volunteering in a hospital is also a good start.

Say bye-bye to the high school GPA. What matters is your college GPA and your prerequisites.
It's great that you are having some volunteer experience over the summer.

Academic-wise is what you need to focus on. Take those AP or IB exams.
Nursing prereqs that count as high school courses are AP psychology, AP English, AP Statistics, and AP Chemistry.
If your school offers AP chem, take it instead of AP biology, AP bio is more for med school majors. If you are taking AP classes as a junior now or even took AP courses as a sophomore, then you've got a great start. Remember, passing the AP course means nothing to your nursing prereqs, in the end, all that matters is passing the AP exam for your nursing prereqs. the AP course is there to help you pass. You should also take up a foreign language. AP Spanish is great, but other languages are nice too like AP chinese. Don't take AP calc. Take AP stats. If your school offers an anatomy and physiology class too, take it. Other classes that will help you are: communications/public speaking, sociology, and biology. If you can handle the course load and stress, then you've really done yourself a great favor in the end when you get to it.

Trust me, I did that when I was in high school and now I'm exempt from some nursing prereqs.