Umat question please help?

ok im a year 13 student - final year at school, hoping to apply to biomedical science in auckland then medical schoo after the first yearl. i can either sit the umat this year, get practice and hopefully the required grade meaning less pressure in first year biomed - or i can sit it next year with another year of learning/experience. what should i do? sitting this year would mean a lot less pressure next year - and would also help if i wanted to apply to monash med school in melbourne. thanks a lot for you help