Do teachers at your high school set aside time after school to help students? Teachers at my D’s school do. It is by choice. Any students can stay after school during those time slots.
If you can afford it, private math/science tutoring is another option.
Do your best. There are a junior year and at least a semester in a senior year for you to improve your grades.
Aim high is good but be realistic. Ivy or not, the competition is fierce these days.