I don't know the exact number, but i've heard that there was quite a number of tickets left.
The Ticnet website says that there's at least 10% of the tickets left. But it said so from the start so it's not that good of an indication.
However, i'm not surprised at all that they have a hard time selling tickets. Given that the majority of Queen fans are (1) over 30, (2) many have families and that the (3) concert date is the 30th of April (Walpurgis night) which is a very popular time for parties/dinners/family events etc - many potential concert goers simply opt out because of other obligations with friends and family.
My guess is that if you moved the concert date a day or two, it would be a quite different story.