I didn't finish in time either and missed out on 6 marks. However, looking at the grade boundaries for last year's biology paper, you could have dropped 11 marks and still get an A*. Whilst I think the grade boundaries will be fairly high this year because a lot of people found the test easy, 5 marks won't be too harsh on your final grade. Furthermore, you have only done one exam, the final grade for core is all three exams totalled up. Maybe try and make sure you finish on time for the other papers and revise plenty - I'm hoping the other science papers are as good as the one we had today. Good luck!