Your stats are EASILY good enough for medicine
I've gone through the process this year so I know a fair bit about how the system works xD So long as you research your chosen medical schools' selection processes then you should easily get a number of interviews. The UKCAT is a test that medicine applicants have to take in the summer before they send off their UCAS application, so it'd be worth "looking into" this now just to get an idea of what it entails. You may also need to sit the BMAT test (again, look this one up) depending on which unis you apply to, but this one's done in the November after you send off your application, so probably not worth worrying about too much for the minute. Your work experience looks good. Try and get involved with anything you can - particularly long-term volunteering, and keep notes of what you see and do, as those will be VERY useful at interview. DOn't feel the need to spend hundreds of pounds on Med Link or anything though, as generally, they don't add anything to your application because universities know that many people wouldn't be able to afford them anyway!
I would advise staying away from universities such as Birmingham and Oxbridge as your GCSEs will make it a little trickier to get into those places as they place quite a lot of emphasis on those, but for pretty much every other medical school, your stats at the minute look really good!
As has already been said, keep your head down and make sure you get As in your AS Levels, and I'd recommend booking your UKCAT for some time late in the summer holidays so you have plenty of time to prepare for it without it clashing with exams.
And just for the record, hardly any med schools ask for 3 science/maths subjects at AS. So long as you take Biology and Chemistry to A2 then you should be fine
If you've got any questions then feel free to PM me :P
And good luck!!!