are these grades good enough?

So I want to apply for medicine with the UMS:
AS maths: 90, 96, 93.
A2 maths modules sat in AS year: 99, 75

Has the B grade messed things up for me? As the 99 is in c3, I now only need to scrape an A in the c4 module I held over to get an A* so I am really pleased with that. I got 12 A*s in my GCSEs and I can't work out whether these results are really good, ok, or pretty bad?
I was feeling good about them until my friend told me how she got full UMS in the AS, and 99 in the A2.
Not only is it the fact that i've got a B, it's more the fact that some of my AS marks are in the low 90s. Not sure if I'm upset or why I'm upset as it's on the better side of what I was expecting.

Can someone please give an indication on my chances of getting into medicine based on these stats?
How slim are my chances of having a competitive application to Oxbridge?