I reckon I'm okay with F451 given I did OCR GCSE Computing, but F452 is a little more worrying. I tend to make stupid mistakes which cost me a lot of marks.
Here's a tip for revision though. Do lots of past papers and make sure you read the mark scheme afterwards to see what the question was actually looking for. OCR have a habit of asking ambiguous questions wanting a specific response, meaning sometimes you may feel your answer is suitable but in their eyes it doesn't answer the question.