165 squares, of which 61 lie on the way through. The other 63 per cent are wrong turns, and that proportion is what makes a maze hard rather than the size of it: a big maze with few branches is solved at a glance.
There is exactly one route between the way in and the way out, and no loops and no squares walled off from the rest. That is a property of how the maze is cut rather than something checked afterwards, which is what makes the answer sheet the answer rather than an answer.
Cut by walking the grid at random and backing up at every dead end, which is the method that gives long winding corridors. The alternatives branch more often, and a maze that branches every second square is a field of short dead ends rather than a puzzle.
The second sheet is the same maze with the route drawn on it. It prints separately, so it can be kept back.