Practicals are no longer required for GCSE sciences, so I wouldn't worry about this aspect of your GCSEs. However, you don't mention what subjects you've done so it would be difficult to advise on whether yours would be sufficient to meet the requirements.
Bear in mind that a number of universities require a minimum number and specify particular subjects. I never did GCSE Chemistry and I found that this ruled me out of a number of universities even though I was doing the A level in chemistry and even though I was a double graduate (I might do the GCSE just for the sake of completeness in June, even my offer isn't dependent on it, as I'm curious to see what I could get without trying!). You never know quite when a lack of a certain number of subjects or a certain subject might hurt your chances - especially as your choice of universities is usually contingent on your UCAT or BMAT score rather than your academics. If your UCAT tanked, you might be more reliant on being able to apply to BMAT universities. Leeds is a BMAT university which gives points per GCSE grade attained so having a certain number may be beneficial to you to pad out your application.
I would say this: if you can find at least 10 medical schools that would take you as is, no further subjects required, I would give your attention to your A levels. You can always re-evaluate after you've got your A level subjects in hand in the event that you don't manage to get any offers. Most people have to apply more than once to medicine anyway, so that extra year can always be used to fill in any academic gaps in your application.