As above, just do three subjects. You don't get "bonus points" for extra A-levels for any medical schools currently that I can think of (I think you used to be able to at QUB but I believe this has changed now). Focus on getting excellent grades in three subjects.
Medicine isn't about overachieving (contrary to popular belief), it's about being extremely efficient in ticking boxes. Tick the box then move on to the next part of the application you can control - which will be work experience (and reflecting on it, not just racking up hours for the sake of it) and preparing for the UCAT (and/or BMAT if applicable), and then preparing for interviews.