sorry your post is a bit confusing, so im goign to assume when u say ur final subject is between bio and chem u mean bio and german.
So yeah my advice, take the scaling out of the equation. Scaling only matters if u get the marks, it wont lift a 20 to anything meaningful. If u enjoy german and r good at it, then sure go ahead. But also take a peek at the prerequires for medicine. I might be wrong so don't quote me but I am assuming that bio 3/4 with a decent SS is needed for medicine...also u can't know if u like medicine without DOING biology sooooooooo. Maybe look at other subjects to see if u can change them? Just cause Bio seems like a pretty vital subject, but if u dont want to drop german than don't drop it either, so maybe choose another subject u dont do as well in/isnt needed. Or do what I am doing and do 7 subjects in year 11, with a language being done at VSL. Just a suggestion and my 2 cents anyway.