hey so i dont have direct experience with the internship program but in general for working with the big companies, they use grades as a cutoff point for their pool of applicants. and thats really all the purpose that grades serve. they would then look at your experiences and involvement. if you can show leadership, communication, customer service and community involvement through your experiences on your resume then that is good.
I my self was not very involved in extracurricular (but i did have some) and was more involved in volunteering outside of school.
Hope that helps