activities in high school

From what you say, you have been plenty active in high school. If you can show that you did more than just show up to do the minimum and get your required hours or take a mission trip (like literally everybody else) then you will be fine. We are looking for members who will step up to take on responsibilities and offices within the sorority and also make us proud in campus organizations and leadership. Demonstrating commitment and responsibility and leadership through philanthropy or paid jobs can be just as good. If your grades are low that's another issue.