Just keep on shadowing, and don't worry too much yet. I only shadowed on the weekends when I was in high school too (and I still only get to go a couple hours a week now that I'm in college most of the time); so, I wouldn't worry about that too much. Get other experiences with as many types of animals as you can too during your breaks and such (farms, shelters, wildlife rescues, etc).
The main thing that I would reccomend is work on getting good grades because that will help you get into a decent undergrad and minimize your debt via scholarships.
Another thing that helped me a lot in college from high school was AP classes. I got a ton of credits from them which means I get to register for classes before other members of my class so I get better times and better proffessors. You might have to retake some science classes, but it will get you out of some core. AP chem helped me tremendously though becuase I had to take gen chem I and II anyways, but they were an easy As and I understood the subject matter better the second time.
