I did OCR biology and never heard any horror stories until I saw on here a few weeks ago.
Just treat it like your other A levels and don't worry too much about it.
Stay focussed in lessons and you should be find.
Biology is difficult because there will never be a stage where you know 'everything' - there will always be an opportunity to go into more detail. This however does not make the exams more difficult.
There are some interesting exam questions, fill in the gap in a paragraph or table and I even saw a crossword in one past paper.
To summarise:
It'll be fine if you work hard - advice which is relevant to all subjects.