You should double check with your school but it isn't likely to make a huge amount of difference. I believe AQA officially suggests a 10% margin either side (ie the word count is really 4500-5500 words), but as far as I know they don't mention any specific penalties for exceeding that.
That said, keeping to the word count is obviously a critical part of the project's execution, and you have to demonstrate that you can plan and fulfil the project in line with the brief and the assessment criteria. Writing 10,000 words would therefore be a clear failure of your ability to manage your project effectively (and you'd really annoy whoever has to mark it), so you would be marked down for it.
I would try to get it to 5,500 if I were you - really focus on your sentences and whether you can phrase things in a simpler way. Also double check to make sure you haven't got any stray references or captions which you're including - they don't count towards the word limit. If you're using an appendix, see if there's any information that you can shift into that - again, the words in the appendix don't count.
It's a good habit to get into because at university you will be penalised if you exceed the word count at all.