Biology and Chemistry A-Level complement each other pretty well but they are both very challenging. Biology A-Level is completely different to GCSE as the sheer breadth and depth of knowledge you need to memorise is insane (not to mention the mark schemes become super picky!) To put this into perspective, your B1 topic is around 13/14 pages long whereas my AS Biology textbook is about 300 pages long and I need to absorb pretty much all of the info on those pages AS WELL AS my 320 page long A2 textbook if I want to get my A/A*.
I managed A*'s in the sciences at GCSE (edexcel) with little trouble and I got quite a shock when I got to A-Level - there is so much to remember! However, if you put the hard work in, revise for a few hours a week (even when you first start in September) by doing tons of past papers and pin-pointing topics on the specification that you struggle with and ask your teacher for extra support on those, there is no reason you can't do well!
As for chemistry, I love it. I find it so logical and there is far less content to cram into your brain than there is for Biology - you just need to make sure you fully grasp all of the concepts and practice using past papers!
I can't speak for Psychology sadly but I'd strongly recommend choosing Biology purely because it will open more doors for you and some courses require it (Med, Dent, Bio-Med). I don't think that there is a course that absolutely requires Psychology A Level (not even a psychology degree!) It will be hard work but if you have a passion for it then that will help you through :-)