You haven’t started yet, so this isn’t a transfer. This is a question about deferring enrollment while you re-think things, or cancelling enrollment entirely and studying somewhere else. You don’t want to start, shell out a boat-load of money and then transfer out to a “cheaper” place because the good merit aid goes to freshmen.
Your instincts are correct. This is too much debt to take on for your undergrad program. Finishing up your BS/MD with something approaching 500k in debt will absolutely control what you can do with your life. Not to mention how ugly your financial situation could be if you should change your career goals mid-way and be saddled with 150k or 200k for just a bachelor’s degree.
Defer or cancel and take a gap year. Reconsider all of your options. The cheap state U could work well for you. If your grades and test scores got you into the BS/MD program, they also are likely to land you serious merit money somewhere else if you start at that other place as a freshman. There is a whole thread at the top of the Financial Aid Forum on the topic of automatic merit scholarships that is worth reading through.