umm.. Well my bmat was ok, but not brilliant.
I got 5.4, 4.6, 12.0 and my UMS marks were all 90%+ and I found that the interview made a massive difference. Seeing as my lower BMAT score was only lacking in section B, which is science knowledge, and I'd shown I can do science at interview/ UMS, I managed to get an offer.
To prepare, I'd advise learning off the GCSE 2000 spec for the science and maths, and the only book I used was preparing for the ukcat and bmat one, but I've heard the bmat specific one is much more helpful (should have bought it, idk why I didn't)..
The BMAT is important, and doing as well as you can is important, but I looked at past statistics and a person scoring under 5 in section B had virtually no chance of getting in, which was really upsetting at the time. But I did it, and I think its the entire application that makes a difference, so work on making everything else flawless.. Like your UMS..