IMPORTANT: starting biology a level halfway through year 12

I do 3 a levels right now: psychology, history and business. But now i want to drop business and do a biology alevel instead. How hard will it be to catch up because half the content for yr 12 has already been taught? Is it worth it. I want to do biology because it then opens up two possible pathways from me (doing psychology at uni and doing law at uni) whereas right now, i only really have 1 option which is law. I talked to my tutor about this and they gave me these 2 options:
1) drop business and start bio (she recommended i take lessons from a private tutor alongside)
2) Do history, psychology and business for yr 12 and 13 and be done with them. And start doing Biology a level in year 13 and then take a gap year and finish the bio a level (think of it as a yr 14).
3) she also said i could do a foundation year in biology before a pychology but then this option isnt very appealing to me because that means that i would have to pay uni fees for basically doing a biology a level (so id rather just go with option 2 instead)