I also did IB, just received my second offer. Did HL bio and chem. my advice would be not to underestimate the syllabus outlines, if you use these and some good concise revision guides, you should be fine. I revised by making detailed notes on every topic for bio, chem is harder so i just did every single past paper i could find and filled in the gaps. So just use the syllabus and do a lot of past papers.