Very sorry to hear that your exams didn't go as well as you'd hoped.
A degree in veterinary nursing will not qualify you to be a veterinary surgeon, no. It is unheard of to transfer onto a veterinary medicine course from another degree.
It is possible to study veterinary medicine as a postgraduate degree, and a degree such as biosciences may enable you to apply for the accelerated vetmed course (4 years instead of 5) at some universities. This route would therefore take 7 years in total, 3 of bioscience and 4 of vet. Bear in mind though that tuition fees for people studying vetmed as a postgrad can reach 30k per year, the postgrad route is just as competitive as the undergrad route, and after all that they may still require A-level/GCSE/Higher etc etc grades anyway.
Your best bet is to resit your exams. Most universities are fine with this although that comment is based on the A-Level requirements (I'm assuming you're Scottish), so double check university websites.
Best of luck!