....and after trying in vain to find the link on their site to display the results in a blog, I did a view-source to see how you'd done it. Right. OK. I could do something similar, but as a note to readers who aren't web coders and don't have their own hosting facilities: stop wasting your time looking.
19/20. Caught out by one of the spelling ones. The whole double-letters thing is one of English's worst "no logic whatsoever" aspects, I have to say. Another contender would be the number of different ways of spelling what's phonetically a schwa, though I tend to file that under "bizarre features of English pronunciation", rather than spelling as such.