Taking a gap year to apply for foundation year medicine but I need A level Biology

So I have only recently decided that I want to do medicine however I have found out that I don't have the required subjects as I am doing Chemistry, Mathematics and Sociology. My GCSE grades for the standard route for medicine A100 is not good enough either which is mainly because I had no real interest in studying in the past and wasn't really motivated by my parents. I got 7,7,7,7,6,6,6,6,5. long story short I am planning on doing the whole of A level Biology course in 1 year during my gap year and also applying in the same year. I was confused on how I would apply through UCAS with the predicted grades since I would be doing the course as a private candidate. I have emailed Plymouth and they have told me I can do the A level Biology in my gap year and still apply in that year with a predicted grade but I am confused as what I have to put the predicted grade as.