Even if you go into college with your major chosen, do you still have to do general studies?
Yes, generally speaking.
Most schools have general education requirements that you have to take regardless of major. Knowing your major ahead of time does not exempt you from these courses.
At the majority of colleges, having a declared major will not get you out of gen eds. Typically only taking APs or community college classes allow you to be exempt from gen ed requirements and many schools cap the number of credits that a student can bring in.