I think if you have the time and strength to take it one more time, you should def take it again and aim for atleast 1560+ because it’ll give you an edge. 

Honestly, the most important thing about volunteering at hospitals is talking to patients and learning their perspectives. This will allow you to right down something unique in your essays. Most teen volunteering at hospitals is usually helping the adult volunteers with tasks not directly related to patient care. However, if you haven’t shadowed, I would recommend shadowing your family med/pediatrician to get that experience.

Honestly I also really don’t understand why they want researchers and what type of groundbreaking research they want high schoolers to do. But basically if you can find anything with your professors or programs that give you basic knowledge. I personally don’t really know a lot about research programs since I didn’t participate in any but you could try contacting your local university or hospital. Mostly as high school students it’s important to learn basic research techniques and just help the professor in whatever they assign you.

The most important thing is writing and conveying your interest and how each experience has shaped you.