If the end goal is medicine, do not do a degree with the sole aim of GEM.
Take a gap year, fix whatever it was that meant you didn't get an offer this time, and reapply.
GEM is *more* competitive, with fewer spaces per applicant than standard. It will cost more, and you'll also be competing against AHPs with years and thousands of hours of clinical experience.
If you do another degree, make sure you would be happy doing that as your job, because statistically speaking you're unlikely to get a GEM place.
Do you know why you got rejected? UCAT/BMAT score? That's fixable enough
Grades? Resit some a levels