I have just finished OCR A2 Biology and I would tell you what I think.
The step-up from GCSE to A-levels is quite intense, both in terms of volume of information you need to learn and the style of answering exam questions, but the step-up from AS to A2 is relatively minor.
It is true that OCR is notorious picky when it come to key words, as so many words are underlined in the mark scheme and there are lots of new technical terms, but as long as you understand the content and able to make the connection between different modules and if you do plenty of past papers as your exam preparation, that should not be an problem to you.
Judging by your A* in GCSE Biology I am sure you are very intelligent and you work very hard, if you can maintain this work ethnics, you will be very successful in A-level Biology.