You're vacillating between nurse and doctor, right? Have you considered PA? I know -- a third option sounds like the last thing you need, but it's honestly sort of an 'in between' position that might offer you a very comfortable and reachable goal, yet with still enough challenge and direct patient interaction to motivate you. And if you change your mind part way through, you'll still be in a good position to go up to MD or down to nursing.
Anyway - to your specific questions:
1 - Will you regret never taking the chance? No one can answer that for you. I would. But others seem to need a 'what if' in their lives...
2 - Should you transfer? If you're doing well at your school and it offers the classes you need (do check on that), then there's really no need to transfer.