Firstly, I wouldn't forget Oxbridge because of those grades. Cambridge yes, but you've got an (admittedly small) chance for Oxford.
And yes, Bristol and UCL are definitely worth applying to. Your AS results are really good! Obviously it would have been better if you got an A in Maths, but I don't think Maths is of critical importance for Biology. I'm not an expert in either university, but I think you're probably a really decent candidate for them.
You've got nothing to lose (apart from money) with respect to the Maths remark. If you've got a high B, then it's virtually impossible for you to drop a grade with a remark because you would have to lose so many points for that to happen. The remark probably isn't going to change anything since there's not really a lot of subjectivity when it comes to Maths so it's unlikely the examiner marked you incorrectly, but there is a small chance that you could be marked up.