UKCAT isnt everything. And it certainly isn't your whole application.
Either apply to Unis like Bristol who put less emphasis on UKCAT and more on your PS, or forget your application to Medicine for this year, work your butt off to get the best grades you can - then retake UKCAT next summer, and apply for Medicine next year for 2019 start.
If you really want to be a doctor then waiting 12 months wont be a big issue.