I know it's a bit late, but there may just be time to apply for a re-mark if you haven't done so already.
EDIT - I've just noticed the original post is from February 2015, not 2017! So it probably is a bit late now But I'll leave my comment up in case it helps anyone else.
First of all, my understanding is that your score can be reduced in a re-mark.
But looking at your marks, even if you only got
5.5 for writing in a re-mark, you would still get an overall band score of 7.5: L 8.5 R 7.5 W 5.5 S 7.5 = average 7.25 which is rounded up to 7.5
However, if you got a
7.5 for writing, your average band score would be 7.75, which is rounded up to 8.0.
So yes, it's worth the risk. The risk of lowering your band score is far less than the chance of increasing your band score.
However, it shouldn't be a case of you thinking you "deserve" a better score, but do you "need" (or "want") a better score. Your overall score is 7.5, which is great. Do you need an 8.0? If you do, go for a re-mark.
I hope this helps!