Do you really have to know exactly what you want to do in college? Can't you just enter college as an undecided student?
Of course you can enter college undecided. Truly, many of the students who enter college as "decided" are not truly definite on what they want to do. However, the extent that it is possible to narrow down what your likely general areas of study in college will be (STEM, Business, Humanities, Social Sciences) helps tremendously in college selection. Colleges differ in focus and the extent to which they offer areas of study. Having a general idea of strength and talent can help families choose the best colleges for a student and minimize the need to transfer later or take an extra year to graduate.