I found rolling the batter into a perfect 8x8 square to be a little tricky. Initially just roll it to 1/2 cm in thickness, then take a knife and outline almost an 8x8 square with a slight indent (via the knife). Don't just cut away the excess. Where the knife made the outline, fold the excess back into the batter and gently roll it out. I did this a few times and my square wasn't perfect but it worked!