Change majors, do a second major, etc. "Assuming I know the relevant programming languages and have some experience" is a big assumption. Computer Science (or any science major) is very hard to pick up part time. For your first job you will be competing with CS grads. I bet it will be an eye opening experience for you since CS grads do get an unfair advantage in the industry. The chances are you will have to take a much less lucrative position and will be playing catch up for many years. Ask yourself - why go that route?
If you decided to do programming - do programming. Consider yourself lucky to have it figured out while you are still in school.
If you decided to do programming - do programming. Consider yourself lucky to have it figured out while you are still in school.