It turns out that I have been doing my word count all wrong! I've been using the Word Count tool in Microsoft Word, whereas there is a different way of doing it that involves the number of words per line and per page, multiplied by the number of pages per chapter. Actually, that's not a very good way of describing it. But anyway, I was given the correct formula by the lovely ladies in the eHarlequin.com community, and have just worked out my 'real' word count.
It's actually 49,125. This means I unknowingly passed the halfway mark some time around chapter eight, and I'm actually now about 61% of the way through the book! Which is kind of good, because as I mentioned previously, I was starting to worry about running out of story, as I'd got a fair way through the story arc but seemed to have many more words still to go to reach the elusive 80,000. Turns not there's not as many more to do now, though!