Your parents 'expect' you, or you 'expect' you?
If you want to do medicine, then do medicine. Nursing is screwed enough without people training who have no plan to actually go in to nursing.
My advice would be to sort it out now. You only get funding for one degree, so if you do nursing and then medicine then you will have to fund medicine yourself. From what I've heard, the DH bursary will not be available for GEP students for much longer - with the potential for one year (final year) of funding. There is also a big grey cloud over whether second degree medics will get student loans past next year. As it stands the only degrees for which you are eligable for a second student loan are ones leading to a vocational qualification (med, dent, vet med, architecture etc). Could you afford to do medicine after a first degree?
Also - there is more competition post-graduate, for both GEP courses and for 5 and 6 year medicine.