I recommend to everyone that you ask for your dissapointing results to get remarked ASAP. I know people who have gone up 2 and even 3 grades.
Because, ~reality check~ the markers are humans who are marking the same thing over and over and they will miss stuff and mark papers incorrectly. In fact, I believe Edexcel had a major rethink of it's markers' training recently because it turned out the majority of the dummy exams they gave their markers were incorrectly marked (and most of the time marked down by too much).
You've nothing to lose!